HemK, a class of protein methyl transferase with similarity to DNA methyl transferases, methylates polypeptide chain release factors, and hemK knockout induces defects in translational termination
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Nakahigashi, K
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Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, JapanKyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Nakahigashi, K
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Kubo, N
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Kubo, N
Narita, S
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Narita, S
Shimaoka, T
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Shimaoka, T
Goto, S
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Goto, S
Oshima, T
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Oshima, T
Mori, H
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Mori, H
Maeda, M
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Maeda, M
Wada, C
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Wada, C
Inokuchi, H
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机构:Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
Inokuchi, H
机构:
[1] Kyoto Univ, Grad Sch Sci, Dept Biophys, Sakyo Ku, Kyoto 6068502, Japan
[2] Japan Sci & Technol Corp, Core Res Evolut Sci & Technol, Ikoma, Nara 6300101, Japan
[3] Nara Inst Sci & Technol, Res & Educ Ctr Genet Informat, Ikoma, Nara 6300101, Japan
[4] Kyoto Univ, Inst Virus Res, Sakyo Ku, Kyoto 6068507, Japan
HemK, a universally conserved protein of unknown function, has high amino acid similarity with DNA-(adenine-N6) methyl transferases (MTases). A certain mutation in hemK gene rescues the photosensitive phenotype of a ferrochelatase-deficient (hemH) mutant in Escherichia coli. A hemK knockout strain of E coli not only suffered severe growth defects, but also showed a global shift in gene expression to anaerobic respiration, as determined by microarray analysis, and this shift may lead to the abrogation of photosensitivity by reducing the oxidative stress. Suppressor mutations that abrogated the growth defects of the hemK knockout strain were isolated and shown to be caused by a threonine to alanine change at codon 246 of polypeptide chain release factor (RF) 2, indicating that hemK plays a role in translational termination. Consistent with such a role, the hemK knockout strain showed an enhanced rate of read-through of nonsense codons and induction of transfer-mRNA-mediated tagging of proteins within the cell. By analysis of the methylation of RF1 and RF2 in vivo and in vitro, we showed that HemK methylates RF1 and RF2 in vitro within the tryptic fragment containing the conserved GGQ motif, and that hemK is required for the methylation within the same fragment of, at least, RF1 in vivo, This is an example of a protein AATase containing the DNA MTase motif and also a protein-(glutamine-N5) MTase.