記述言語：英語   掲載種別：研究論文（学術雑誌）  

To investigate RNA degradation in live cells, detection methods that do not require RNA extraction from cells are necessary. In this study, we examined the utility of fluorescence lifetime measurements using a probe attached to the end of an RNA molecule for detecting RNA degradation. We optimized a short fluorescein-labeled RNA sequence whose fluorescence lifetime varied significantly before and after degradation. The selected HHG-fluorescein sequence (H = U, C, or A) is a promising RNA labeling unit (fluorescence lifetime probe) for live cell imaging of RNA degradation.

DOI： 10.1039/d0an01230k

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Investigation of the relevance between cell cycle status and the bioactivity of exogenously delivered biomacromolecules is hindered by their time-consuming cell internalization and the cytotoxicity of transfection methods. In this study, we addressed these problems by utilizing the photochemical internalization (PCI) method using a peptide/protein-photosensitizer conjugate, which enables immediate cytoplasmic internalization of the bioactive peptides/proteins in a light-dependent manner with low cytotoxicity. To identify the cell-cycle dependent apoptosis, a TatBim peptide-photosensitizer conjugate (TatBim-PS) with apoptotic activity was photo-dependently internalized into HeLa cells expressing a fluorescent ubiquitination-based cell cycle indicator (Fucci2). Upon irradiation, cytoplasmic TatBim-PS internalization exceeded 95% for all cells classified in the G1, S, and G2/M cell cycle phases with no significant differences between groups. TatBim-PS-mediated apoptosis was more efficiently triggered by photoirradiation in the G1/S transition than in the G1 and S/G2/M phases, suggesting high sensitivity of the former phase to Bim-induced apoptosis. Thus, the cell cycle dependence of Bim peptide-induced apoptosis was successfully investigated using Fucci2 indicator and the PCI method. Since PCI-mediated cytoplasmic internalization of peptides is rapid and does not span multiple cell cycle phases, the Fucci-PCI method constitutes a promising tool for analyzing the cell cycle dependence of peptides/protein functions.

DOI： 10.1038/s41598-020-76100-7

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Cell-penetrating peptides (CPPs) are widely used for the intracellular delivery of peptides and proteins, but CPP fusion peptides and proteins are often transported by endocytosis and trapped in endosomes. Photochemical internalization (PCI) is a method for the endosomal escape of the trapped peptide or protein and release into the cytosol using light and photosensitizers. In PCI, endosomal membranes are thought to be destabilized by singlet oxygen (1O2) photogenerated from photosensitizers localized in endosomes. We previously developed CPP-cargo-photosensitizer (PS) conjugates able to photodependently enter the cytosol via the PCI mechanism. For example, TatU1A-PS (a covalent complex of Tat [CPP], U1A RNA-binding protein [cargo], and PS) can photodependently deliver RNAs into the cytosol, and TatBim-PS (a covalent complex of Tat, Bim [cargo], and PS) can photoinduce apoptosis in mammalian cells. However, for many newly created conjugates, the induction of PCI has been insufficient. We hypothesized that the amino acid linker sequence (XX) adjacent to the photosensitizer is an important determinant of PCI efficiency. In this study, using CPP-cargo-XX-PS platforms, we examined the relationship between PCI efficiency and the linker amino acid sequence near the photosensitizer. We found that hydrophobic FF and LL linkers enhanced the PCI efficiencies of both TatBim-XX-PS and TatU1A-XX-PS. The effectiveness of the linker depended, in part, on both the cargo moiety and the photosensitizer. These results may guide the design of CPP-cargo-PS conjugates conferring broad target functions for PCI and photodynamic therapy.

DOI： 10.1021/acs.bioconjchem.0c00046

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

The inefficient endosomal escape of drugs or macromolecules is a major obstacle to achieving successful delivery to therapeutic targets. An efficient approach to circumvent this barrier is photochemical internalization (PCI), which uses light and photosensitizers for endosomal escape of the delivered macromolecules. The PCI mechanism is related to photogenerated singlet oxygen, but the mechanism is still unclear. In this study, we examined the relation of PCI to heat, pH and Ca2+ ions using cell penetrating peptide (CPP)-cargo-photosensitizer (Alexa546 or Alexa633) conjugates. A cell temperature changing experiment demonstrated that heat (thermal mechanism) does not significantly contribute to the photoinduced endosomal escape. Inhibition of V-ATPase proton pump activity and endosomal pH upregulation indicated that PCI-mediated endosomal escape needs endosomal acidification prior to photoirradiation. Imaging of the CPP-cargo-photosensitizer and Ca2+ ions during photostimulation showed that intracellular calcium increase is not the cause of the endosomal escape of the complex. The increment is mainly due to Ca2+ influx. These findings show the importance of extra- and intracellular milieu conditions in the PCI mechanism and enrich our understanding of PCI-related changes in cell.

DOI： 10.1111/php.13146

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担当区分：最終著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Cellular functions are regulated by the up- and down-regulation and localization of RNA molecules. Therefore, many RNA detection methods have been developed to analyze RNA levels and localization. Molecular beacon (MB) is one of the major methods for quantitative RNA detection and analysis of RNA localization. Most oligonucleotide-based probes, including MB, are designed to target a long flexible region on the target RNA molecule, e.g., a single-stranded region. Recently, analyses of tRNA localization and levels became important, as it has been shown that environmental stresses and chemical reagents induce nuclear accumulation of tRNA and tRNA degradation in mammalian cells. However, tRNA is highly structured and does not harbor any long flexible regions. Hence, only a few methods are currently available for detecting tRNA. In the present study, we attempted to detect elongator tRNAMet (eMet) and initiator tRNAMet (iMet) by using an in-stem molecular beacon (ISMB), characterized by more effective quenching and significantly higher sensitivity than those of conventional MB. We found that ISMB1 targeted a 5'- region that includes the D arm of tRNA and that it detected eMet and iMet transcripts as well as mature eMet with high sensitivity. Moreover, the analysis revealed that the formation of the ISMB/tRNA transcript complex required more time than the formation of an ISMB/unstructured short RNA complex. These results suggest that ISMB-based tRNA detection can be a useful tool for various biological and medical studies.

DOI： 10.1371/journal.pone.0211505

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Many cellular events are thought to be controlled by the temporal upregulation of multiple RNAs; the timing of the upregulation of these RNAs is not always the same. In this study, we first show that our light-directed intracellular RNA delivery method induced high concentrations of RNA in a short period. This effect was beneficial for the temporal control of cellular events by functional RNAs. Next, we stimulated the short-term upregulation of two different RNAs at different time points. Cytosolic delivery of a first RNA was induced by red light; thereafter, cytosolic delivery of a second RNA was induced by near-infrared light. The time difference between the introduction of the first and second RNA can be short (0.5-4 h) or long (>8 h). This strategy shows the potential for future applications of the deliberate control of time-dependent RNA concentration to guide various cellular functions by multiple RNAs.

DOI： 10.1021/acs.bioconjchem.8b00487

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Blackwell Publishing Ltd  

MicroRNAs (miRNAs) belong to a class of small noncoding RNAs that play important roles in the translational regulation of gene expression. A number of miRNAs are known to act as key regulators of diverse processes such as neuronal differentiation. In this study, we have attempted to identify novel miRNAs related to neuronal differentiation via microarray analysis in the human neuronal differentiation model neuroblastoma SH-SY5Y cells. We identified 15 up-regulated and eight down-regulated miRNAs in SH-SY5Y cells treated with all-trans retinoic acid to induce differentiation. We further showed that one of the up-regulated miRNAs, miR-664a-5p, promoted neuronal differentiation of SH-SY5Y cells. These findings enhance our understanding of the miRNAs involved in the process of neurogenesis and, in particular, highlight an important role of miR-664a-5p in SH-SY5Y cell neuronal differentiation. Further studies will be required to confirm the function of miR-664-5p in neuronal development and disease and to identify its relevant target genes.

DOI： 10.1111/gtc.12559

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

A method to induce cytoplasmic peptide delivery, using ultrasound, was demonstrated using a molecular conjugate of a cell-penetrating peptide (CPP), a functional peptide, and a sonosensitizer. As a model of such molecular conjugates, TatBim-RB, consisting of the Tat CPP, the Bim apoptosis inducing peptide, and the sonosensitizer rose bengal was synthesized. CPPs have been widely used for intracellular delivery of various cargos; however, CPP-fused molecules tend to become entrapped in endosomes, as was observed for TatBim-RB molecules applied to cells. To promote escape of the entrapped TatBim-RB molecules, cells were irradiated with ultrasound, which successfully induced endosomal escape and cytoplasmic dispersion of TatBim-RB, and subsequently apoptosis. Our results suggest that this peptide-sonosensitizer conjugate strategy may facilitate numerous kinds of medicinal chemistry studies, and furthermore, this specific conjugate may exhibit potential as a novel therapeutic agent for the promotion of apoptosis.

DOI： 10.1016/j.bmc.2017.06.024

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ROYAL SOC CHEMISTRY  

The use of molecular beacons is a versatile method to detect RNAs. Typically, a single-stranded region of RNA is selected as a target sequence for molecular beacons. Therefore, the detection of highly structured short RNAs, such as tRNAs, seems to be difficult. In this study, as an example of highly structured target RNA, we used human tRNA(Lys3), which is known to have functions in protein synthesis and the reverse transcription of human immunodeficiency virus (HIV)-1. No long single-stranded region more than 8 nt is present in this tRNA, which is much shorter than the standard target length of molecular beacons (similar to 20 nt). This study showed that sensitive detection of highly structured RNAs using molecular beacons was much more difficult than that of unstructured or less structured RNAs. However, efficient detection of the tRNA(Lys3) was achieved by selecting the best target region, i.e., the region around the D arm, probably due to the ease of unfolding of this arm. Accordingly, our findings suggested that molecular beacons may have applications in the detection of highly structured RNAs related to various biological functions and diseases.

DOI： 10.1039/c7ay00341b

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担当区分：最終著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

The possibility of spatiotemporally photocontrolling translation holds considerable promise for studies on the biological roles of local translation in cells and tissues. Here we report caged aminoacyl-tRNAs (aa-tRNAs) synthesized using a (7-diethylaminocoumarin-4-yl)methoxycarbonyl (DEACM)-cage compound. DEACM-caged aa-tRNA does not spontaneously deacylate for at least 4 h in neutral aqueous solution, and does not bind to the elongation factor Tu. On irradiation at ∼405 nm at 125 mW cm(-2), DEACM-aa-tRNA is converted into active aa-tRNA with a half-life of 19 s. Notably, this rapid uncaging induced by visible light does not impair the translation system. Translation is photoinduced when DEACM-aa-tRNA carrying a CCCG or a CUA anticodon is uncaged in the presence of mRNAs harbouring a CGGG four-base codon or a UAG amber codon, respectively. Protein synthesis is phototriggered in several model systems, including an in vitro translation system, an agarose gel, in liposomes and in mammalian cells.

DOI： 10.1038/ncomms12501

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

A novel molecule, TatBim-Alexa, consisting of the HIV1 Tat cell-penetrating peptide, the Bim apoptosis-inducing peptide, and Alexa Fluor 546 was synthesized for photoinducion of apoptosis. The Alexa Fluor 546 was used as a photosensitizer and covalently attached at the C-terminus of TatBim peptide by the thiol-maleimide reaction. Photo-dependent cytosolic internalization of TatBim-Alexa and photo-dependent apoptosis using TatBim-Alexa were demonstrated in several kinds of mammalian cells including human cancer cell lines.

DOI： 10.1016/j.bmcl.2016.04.091

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Thermus thermophilus is an extreme-thermophilic eubacterium, which grows at a wide range of temperatures (50-83°C). This thermophile produces various polyamines including long and branched polyamines. In tRNAs from T. thermophilus, three distinct modifications, 2'-O-methylguanosine at position 18 (Gm18), 5-methyl-2-thiouridine at position 54 and N(1)-methyladenosine at position 58, are assembled at the elbow region to stabilize the L-shaped tRNA structure. However, the structures of unmodified tRNA precursors are disrupted at high temperatures. We hypothesize that polyamine(s) might have a positive effect on the modification process of unmodified tRNA transcript. We investigated the effects of eight polyamines on Gm18 formation in the yeast tRNA(Phe) transcript by tRNA (Gm18) methyltransferase (TrmH). Higher concentrations of linear polyamines inhibited TrmH activity at 55°C, while optimum concentration increased TrmH activity at 45-75°C. Exceptionally, caldohexamine, a long polyamine, did not show any positive effect on the TrmH activity at 55°C. However, temperature-dependent experiments revealed that 1 mM caldohexamine increased TrmH activity at 60-80°C. Furthermore, 0.25 mM tetrakis(3-aminopropy)ammonium, a branched polyamine, increased TrmH activity at a broad range of temperatures (40-85°C). Thus, caldohexamine and tetrakis(3-aminopropy)ammonium were found to enhance the TrmH activity at high temperatures.

DOI： 10.1093/jb/mvv130

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：TAYLOR & FRANCIS LTD  

Polymeric micelles that are composed of synthetic polymers are generally size controllable and can be easily modified for various applications. Lactosomes (A3B-type) are biodegradable polymeric micelles composed of an amphipathic polymer, including three poly(sarcosine) blocks and a poly(l-lactic acid) block. Lactosomes accumulate in tumors in vivo through the enhanced permeability and retention (EPR) effect, even on frequently administering them. However, lactosomes cannot be efficiently internalized by cells. To improve cellular uptake of lactosomes, cell-penetrating peptide (CPP)-modified lactosomes were prepared. Seven CPPs (including EB1 and Pep1) were used, and most of them improved the cellular uptake efficiency of lactosomes. In particular, EB1- and Pep1-modified lactosomes were efficiently internalized by cells. In addition, by using CPP-modified and photosensitizer-loaded lactosomes, we demonstrated the photoinduced killing of mammalian cells, including human cancer cells. Accumulation of the EB1-modified lactosomes in NCI-N87 tumors was shown by in vivo imaging. Thus, this study demonstrated that the CPP-modified lactosome is a promising drug carrier.

DOI： 10.1080/14686996.2016.1178056

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

In many drug delivery strategies, an inefficient transfer of macromolecules such as proteins and nucleic acids to the cytosol often occurs because of their endosomal entrapment. One of the methods to overcome this problem is photochemical internalization, which is achieved using a photosensitizer and light to facilitate the endosomal escape of the macromolecule. In this study, we examined the molecular mechanism of photochemical internalization of cell penetrating peptide-cargo (macromolecule)-photosensitizer conjugates. We measured the photophysical properties of eight dyes (photosensitizer candidates) and determined the respective endosomal escape efficiencies using these dyes. Correlation plots between these factors indicated that the photogenerated (1)O2 molecules from photosensitizers were highly related to the endosomal escape efficiencies. The contribution of (1)O2 was confirmed using (1)O2 quenchers. In addition, time-lapse fluorescence imaging showed that the photoinduced endosomal escape occurred at a few seconds to a few minutes after irradiation (much longer than (1)O2 lifetime), and that the pH increased in the endosome prior to the endosomal escape of the macromolecule.

DOI： 10.1038/srep18577

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD  

Translation systems with four-base codons provide a powerful strategy for protein engineering and protein studies because they enable site-specific incorporation of non-natural amino acids into proteins. In this study, a caged aminoacyl-tRNA with a four-base anticodon was synthesized. The caged aminoacyl-tRNA contains a photocleavable nitroveratryloxycarbonyl (NVOC) group. This study showed that the caged aminoacyl-tRNA was not deacylated, did not bind to EF-Tu, and was activated by light. Photo-dependent translation of an mRNA containing the four-base codon was demonstrated using the caged aminoacyl-tRNA.

DOI： 10.1016/j.bmcl.2014.10.053

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Stress induces various responses, including translational suppression and tRNA degradation in mammals. Previously, we showed that heat stress induces degradation of initiator tRNA(Met) (iMet) through 5'-3' exoribonuclease Xrn1 and Xrn2, respectively. In addition, we found that rapamycin inhibits the degradation of iMet under heat stress conditions. Here, we report that the mammalian target of rapamycin (mTOR) regulates the diffusion of Xrn2 from the nucleolus to the nucleoplasm, facilitating the degradation of iMet under conditions of heat stress. Our results suggest a mechanism of translational suppression through mTOR-regulated iMet degradation in mammalian cells.

DOI： 10.1016/j.febslet.2014.08.003

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Controlled activation of small RNAs, such as small interfering RNA, in cells is very useful for various biological applications. Light is an effective inducer of controlled activation; in particular, near-infrared light is favorable because it can penetrate deeper into tissues than UV or visible light. In this study, near-infrared light control of RNA interference (RNAi) was demonstrated in mammalian cells using a photosensitive RNA carrier molecule, consisting of an RNA carrier protein and a fluorochrome. The photosensitive carrier molecule was identified from six candidates, each with a different fluorochrome. Using this carrier molecule, cytosolic RNA delivery and RNAi can be triggered by near-infrared light. Cytotoxicity was not observed after photoinduction of RNAi.

DOI： 10.1021/bc4001195

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

A conserved guanosine at position 18 (G18) in the D-loop of tRNAs is often modified to 2'-O-methylguanosine (Gm). Formation of Gm18 in eubacterial tRNA is catalyzed by tRNA (Gm18) methyltransferase (TrmH). TrmH enzymes can be divided into two types based on their substrate tRNA specificity. Type I TrmH, including Thermus thermophilus TrmH, can modify all tRNA species, whereas type II TrmH, for example Escherichia coli TrmH, modifies only a subset of tRNA species. Our previous crystal study showed that T. thermophilus TrmH is a class IV S-adenosyl-l-methionine-dependent methyltransferase, which maintains a topological knot structure in the catalytic domain. Because TrmH enzymes have short stretches at the N and C termini instead of a clear RNA binding domain, these stretches are believed to be involved in tRNA recognition. In this study, we demonstrate by site-directed mutagenesis that both N- and C-terminal regions function in tRNA binding. However, in vitro and in vivo chimera protein studies, in which four chimeric proteins of type I and II TrmHs were used, demonstrated that the catalytic domain discriminates substrate tRNAs from nonsubstrate tRNAs. Thus, the N- and C-terminal regions do not function in the substrate tRNA discrimination process. Pre-steady state analysis of complex formation between mutant TrmH proteins and tRNA by stopped-flow fluorescence measurement revealed that the C-terminal region works in the initial binding process, in which nonsubstrate tRNA is not excluded, and that structural movement of the motif 2 region of the catalytic domain in an induced-fit process is involved in substrate tRNA discrimination.

DOI： 10.1074/jbc.M113.485128

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Stress response mechanisms that modulate the dynamics of tRNA degradation and accumulation from the cytoplasm to the nucleus have been studied in yeast, the rat hepatoma and human cells. In the current study, we investigated tRNA degradation and accumulation in HeLa cells under various forms of stress. We found that initiator tRNA(Met) (tRNA(iMet)) was specifically degraded under heat stress. Two exonucleases, Xrn1 and Xrn2, are involved in the degradation of tRNA(iMet) in the cytoplasm and the nucleus, respectively. In addition to degradation, we observed accumulation of tRNA(iMet) in the nucleus. We also found that the mammalian target of rapamycin (mTOR), which regulates tRNA trafficking in yeast, is partially phosphorylated at Ser2448 in the presence of rapamycin and/or during heat stress. Our results suggest phosphorylation of mTOR may correlate with accumulation of tRNA(iMet) in heat-treated HeLa cells.

DOI： 10.1093/nar/gkt153

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ACADEMIC PRESS INC ELSEVIER SCIENCE  

The stress response, which can trigger various physiological phenomena, is important for living organisms. For instance, a number of stress-induced granules such as P-body and stress granule have been identified. These granules are formed in the cytoplasm under stress conditions and are associated with translational inhibition and mRNA decay. In the nucleus, there is a focus named nuclear stress body (nSB) that distinguishes these structures from cytoplasmic stress granules. Many splicing factors and long non-coding RNA species localize in nSBs as a result of stress. Indeed, tRNAs respond to several kinds of stress such as heat, oxidation or starvation. Although nuclear accumulation of tRNAs occurs in starved Saccharomyces cerevisiae, this phenomenon is not found in mammalian cells. We observed that initiator tRNA(Met) (Meti) is actively translocated into the nucleus of human cells under heat stress. During this study, we identified unique granules of Meti that overlapped with nSBs. Similarly, elongator tRNA(Met) was translocated into the nucleus and formed granules during heat stress. Formation of tRNA granules is closely related to the translocation ratio. Then, all tRNAs may form the specific granules.

DOI： 10.1016/j.bbrc.2011.12.150

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

CCA-adding enzyme builds the 3'-end CCA of tRNA without a nucleic acid template. The mechanism for the maintenance of fidelity during the CCA-adding reaction remains elusive. Here, we present almost a dozen complex structures of the class I CCA-adding enzyme and tRNA mini-helices (mini-D(73)N(74), mini-D(73)N(74)C(75) and mini-D(73)C(74)N(75); D(73) is a discriminator nucleotide and N is either A, G, or U). The mini-D(73)N(74) complexes adopt catalytically inactive open forms, and CTP shifts the enzymes to the active closed forms and allows N(74) to flip for CMP incorporation. In contrast, unlike the catalytically active closed form of the mini-D(73)C(74)C(75) complex, the mini-D(73)N(74)C(75) and mini-D(73)C(74)N(75) complexes adopt inactive open forms. Only the mini-D(73)C(74)U(75) accepts AMP to a similar extent as mini-D(73)C(74)C(75), and ATP shifts the enzyme to a closed, active form and allows U(75) to flip for AMP incorporation. These findings suggest that the 3'-region of RNA is proofread, after two nucleotide additions, in the closed, active form of the complex at the AMP incorporation stage. This proofreading is a prerequisite for the maintenance of fidelity for complete CCA synthesis.

DOI： 10.1038/emboj.2008.124

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Eubacterial leucyl/phenylalanyl-tRNA protein transferase (LF-transferase) catalyses peptide-bond formation by using Leu-tRNA(Leu) (or Phe-tRNA(Phe)) and an amino-terminal Arg (or Lys) of a protein, as donor and acceptor substrates, respectively. However, the catalytic mechanism of peptide-bond formation by LF-transferase remained obscure. Here we determine the structures of complexes of LF-transferase and phenylalanyl adenosine, with and without a short peptide bearing an N-terminal Arg. Combining the two separate structures into one structure as well as mutation studies reveal the mechanism for peptide-bond formation by LF-transferase. The electron relay from Asp 186 to Gln 188 helps Gln 188 to attract a proton from the alpha-amino group of the N-terminal Arg of the acceptor peptide. This generates the attacking nucleophile for the carbonyl carbon of the aminoacyl bond of the aminoacyl-tRNA, thus facilitating peptide-bond formation. The protein-based mechanism for peptide-bond formation by LF-transferase is similar to the reverse reaction of the acylation step observed in the peptide hydrolysis reaction by serine proteases.

DOI： 10.1038/nature06167

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Eubacterial leucyl/phenylalanyl-tRNA protein transferase (L/F-transferase), encoded by the aat gene, conjugates leucine or phenylalanine to the N-terminal Arg or Lys residue of proteins, using Leu-tRNA(Leu) or Phe-tRNA(Phe) as a substrate. The resulting N-terminal Leu or Phe acts as a degradation signal for the ClpS-ClpAP-mediated N-end rule protein degradation pathway. Here, we present the crystal structures of Escherichia coli L/F-transferase and its complex with an aminoacyl-tRNA analog, puromycin. The C-terminal domain of L/F-transferase consists of the GCN5-related N-acetyltransferase fold, commonly observed in the acetyltransferase superfamily. The p-methoxybenzyl group of puromycin, corresponding to the side chain of Leu or Phe of Leu-tRNA(Leu) or Phe-tRNA(Phe), is accommodated in a highly hydrophobic pocket, with a shape and size suitable for hydrophobic amino-acid residues lacking a branched beta-carbon, such as leucine and phenylalanine. Structure-based mutagenesis of L/F-transferase revealed its substrate specificity. Furthermore, we present a model of the L/F-transferase complex with tRNA and substrate proteins bearing an N-terminal Arg or Lys.

DOI： 10.1038/sj.emboj.7601433

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

Transfer RNA (Gm18) methyltransferase (TrmH) catalyzes the methyl transfer from S-adenosyl-L-methionine (AdoMet) to the 2'-OH group of the G18 ribose in tRNA. To identify amino acid residues responsible for the tRNA recognition, we have carried out the alanine substitution mutagenesis of the basic amino acid residues that are conserved only in TrmH enzymes and not in the other SpoU proteins. We analyzed the mutant proteins by S-adenosyl-L-homocysteine affinity column chromatography, gel mobility shift assay, and kinetic assay of the methyl transfer reaction. Based on these biochemical studies and the crystal structure of TrmH, we found that the conserved residues can be categorized according to their role (i) in the catalytic center (Arg-41), (ii) in the initial site of tRNA binding (Lys-90, Arg-166, Arg-168, and Arg-176), (iii) in the tRNA binding site required for continuation the catalytic cycle (Arg-8, Arg-19, and Lys-32), (iv) in the structural element involved in release of S-adenosyl-L-homocysteine (Arg-11-His-71-Met-147 interaction), (v) in the assisted phosphate binding site (His-34), or (vi) in an unknown function (Arg-109). Furthermore, the difference between the Kd and Km values for tRNA suggests that the affinity for tRNA is enhanced in the presence of AdoMet. To confirm this idea, we carried out the kinetic studies, a gel mobility shift assay with a mutant protein disrupted in the catalytic center, and the analytical gel-filtration chromatography. Our experimental results clearly show that the enzyme has a semi-ordered sequential mechanism in which AdoMet both enhances the affinity for tRNA and induces formation of the tetramer structure.

DOI： 10.1074/jbc.M606141200

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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

Transfer RNA (Gm18) methyltransferase (TrmH (SpoU)) catalyzes the transfer of a methyl group from S-adenosyl-l-methionine (AdoMet) to the 2'-OH of guanosine 18 in tRNA. This enzyme is a member of the SpoU family of RNA methyltransferases. Recent computational researches have shown that three amino acid sequence motifs are conserved among the SpoU members. Recently, we determined the crystal structures of the apoand AdoMet bound forms of TrmH (Nureki, O., Watanabe, K., Fukai, S., Ishii, R., Endo, Y., Hori, H., and Yokoyama, S. (2004) Structure 12, 593-602). Furthermore, we clarified the AdoMet binding site and proposed the catalytic mechanism. Since the functions of the conserved amino acid residues in the motifs remain unknown, here we have prepared 17 mutants of TrmH and carried out various biochemical studies, including determination of the kinetic parameters for both AdoMet and tRNA, S-adenosyl-l-homocysteine affinity chromatography, gel mobility shift assay, CD spectroscopy, and analytical gel filtration. Our results show that Asn(35), Arg(41), Glu(124), and Asn(152) are involved in binding tRNA and that the Asn(35) residue is involved in the release of S-adenosyl-l-homocysteine. Several residues of TrmH are important for stability of the enzyme. Taken together, our biochemical studies reinforce the previously proposed catalytic mechanism. We also discuss amino acid substitutions in general within the SPOUT superfamily of methyltransferases.

DOI： 10.1074/jbc.M411209200

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

Transfer RNA (m7G46) methyltransferase catalyzes the methyl transfer from S-adenosylmethionine to N7 atom of the guanine 46 residue in tRNA. Analysis of the Aquifex aeolicus genome revealed one candidate open reading frame, aq065, encoding this gene. The aq065 protein was expressed in Escherichia coli and purified to homogeneity on 15% SDS-polyacrylamide gel electrophoresis. Although the overall amino acid sequence of the aq065 protein differs considerably from that of E. coli YggH, the purified aq065 protein possessed a tRNA (m7G46) methyltransferase activity. The modified nucleoside and its location were determined by liquid chromatography-mass spectroscopy. To clarify the RNA recognition mechanism of the enzyme, we investigated the methyl transfer activity to 28 variants of yeast tRNAPhe and E. coli tRNAThr. It was confirmed that 5'-leader and 3'-trailer RNAs of tRNA precursor are not required for the methyl transfer. We found that the enzyme specificity was critically dependent on the size of the variable loop. Experiments using truncated variants showed that the variable loop sequence inserted between two stems is recognized as a substrate, and the most important recognition site is contained within the T stem. These results indicate that the L-shaped tRNA structure is not required for methyl acceptance activity. It was also found that nucleotide substitutions around G46 in three-dimensional core decrease the activity.

DOI： 10.1074/jbc.M408209200

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：CELL PRESS  

The tRNA(Gm18) methyltransferase (TrmH) catalyzes the 2'-O methylation of guanosine 18 (Gua18) of tRNA. We solved the crystal structure of Thermus thermophilus TrmH complexed with S-adenosyl-L-methionine at 1.85 A resolution. The catalytic domain contains a deep trefoil knot, which mutational analyses revealed to be crucial for the formation of the catalytic site and the cofactor binding pocket. The tRNA dihydrouridine(D)-arm can be docked onto the dimeric TrmH, so that the tRNA D-stem is clamped by the N- and C-terminal helices from one subunit while the Gua18 is modified by the other subunit. Arg41 from the other subunit enters the catalytic site and forms a hydrogen bond with a bound sulfate ion, an RNA main chain phosphate analog, thus activating its nucleophilic state. Based on Gua18 modeling onto the active site, we propose that once Gua18 binds, the phosphate group activates Arg41, which then deprotonates the 2'-OH group for methylation.

DOI： 10.1016/j.str.2004.03.003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC  

Transfer RNA (guanosine-2')-methyltransferase (Gm-methylase) catalyzes the transfer of a methyl group from S-adenosyl-l-methionine to 2'-OH of G18 in the D-loop of tRNA. Based on their mode of tRNA recognition, Gm-methylases can be divided into the following two types: type I having broad specificity toward the substrate tRNA, and type II that methylates only limited tRNA species. Protein synthesized by in vitro cell-free translation revealed that Gm-methylase encoded in the Aquifex aeolicus genome is a novel type II enzyme. Experiments with chimeric tRNAs and mini- and micro-helix RNAs showed that the recognition region of this enzyme is included within the D-arm structure of tRNALeu and that a bulge is essentially required. Variants of tRNALeu, tRNASer, and tRNAPhe revealed that a combination of certain base pairs in the D-stem is strongly recognized by the enzyme, that 4 bp in the D-stem enhance methyl acceptance activity, and that the Py16Py17G18G19 sequence is important for efficient methyl transfer. The methyl acceptance activities of all the A. aeolicus tRNA genes, which can be classified into 14 categories on the basis of their D-arm structure, were tested. The results clearly showed that the substrate recognition mechanism elucidated by the variant experiments was applicable to their native substrates.

DOI： 10.1074/jbc.M212577200

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（商業誌、新聞、ウェブメディア）  

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）  

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記述言語：日本語   出版者・発行元：日本DDS学会  

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記述言語：英語   出版者・発行元：ELSEVIER ACADEMIC PRESS INC  

Small interfering RNA (siRNA) and short hairpin RNA (shRNA) may potentially treat a wide variety of diseases through RNA interference-mediated silencing of specific genes. MicroRNAs (miRNAs) are endogenous regulatory RNA molecules that also modulate gene expression, and thus potential therapeutic approaches using miRNAs have attracted attention. For clinical application of these small RNAs, efficient and safe RNA delivery to target tissues and cells is necessary. Current challenges to RNA delivery are the penetration of negatively charged RNAs through the cell membrane and specific delivery of RNA into target cells. Photocontrolled intracellular RNA delivery is a promising strategy with high target specificity. This strategy includes photodependent endosomal escape of RNA or photodependent release of RNAs from carrier particles. In this chapter, photocontrolled intracellular RNA delivery methods employing gold or silver nanoparticles, upconversion nanoparticles, proteins, or polymers are discussed.

DOI： 10.1016/bs.pmbts.2015.10.013

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記述言語：日本語  

J-GLOBAL

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記述言語：英語   掲載種別：記事・総説・解説・論説等（学術雑誌）  

DOI： 10.1007/978-94-017-8896-0_19

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記述言語：日本語  

J-GLOBAL

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J-GLOBAL

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（その他）  

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記述言語：日本語   掲載種別：書評論文，書評，文献紹介等  

Scopus

PubMed

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（商業誌、新聞、ウェブメディア）  

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記述言語：日本語  

J-GLOBAL

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会議種別：口頭発表（一般）  

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会議種別：ポスター発表  

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記述言語：日本語   会議種別：口頭発表（招待・特別）  

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会議種別：ポスター発表  

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会議種別：シンポジウム・ワークショップ パネル（指名）  

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会議種別：口頭発表（一般）  

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記述言語：日本語   会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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会議種別：公開講演，セミナー，チュートリアル，講習，講義等  

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会議種別：口頭発表（一般）  

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会議種別：口頭発表（一般）  

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