Involvement of the Escherichia coli folate-binding protein YgfZ in RNA modification and regulation of chromosomal replication initiation

Authors

  • Tomotake Ote,

    1. Department of Biology, Graduate School of Science, Tokyo Metropolitan University, Minamiohsawa, Hachioji, Tokyo 192-0397, Japan.
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  • Masayuki Hashimoto,

    1. Department of Biology, Graduate School of Science, Tokyo Metropolitan University, Minamiohsawa, Hachioji, Tokyo 192-0397, Japan.
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  • Yoshiho Ikeuchi,

    1. Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, Hongo, Tokyo 113, Japan.
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  • Masayuki Su’etsugu,

    1. Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
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  • Tsutomu Suzuki,

    1. Department of Chemistry and Biotechnology, Graduate School of Engineering, University of Tokyo, Hongo, Tokyo 113, Japan.
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  • Tsutomu Katayama,

    1. Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
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  • Jun-ichi Kato

    Corresponding author
    1. Department of Biology, Graduate School of Science, Tokyo Metropolitan University, Minamiohsawa, Hachioji, Tokyo 192-0397, Japan.
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*E-mail jkato@comp.metro-u.ac.jp; Tel. (+81) 426 77 2569; Fax (+81) 426 77 2569.

Summary

The Escherichia coli hda gene codes for a DnaA-related protein that is essential for the regulatory inactivation of DnaA (RIDA), a system that controls the initiation of chromosomal replication. We have identified the ygfZ gene, which encodes a folate-binding protein, as a suppressor of hda mutations. The ygfZ null mutation suppresses an hda null mutation. The over-initiation and abortive elongation phenotypes conferred by the hda mutations are partially suppressed in an hda ygfZ background. The accumulation of the active form of DnaA, ATP-DnaA, in the hda mutant is suppressed by the disruption of the ygfZ gene, indicating that YgfZ is involved in regulating the level of ATP-DnaA. Although ygfZ is not an essential gene, the ygfZ disruptant grows slowly, especially at low temperature, demonstrating that this gene is important for cellular proliferation. We have identified mnmE (trmE) as a suppressor of the ygfZ disruption. This gene encodes a GTPase involved in tRNA modification. Examination of RNA modification in the ygfZ mutant reveals reduced levels of 2-methylthio-6-iodeadenosine, indicating that YgfZ participates in the methylthio-group formation of this modified nucleoside in some tRNAs. These results suggest that YgfZ is a key factor in regulatory networks that act via tRNA modification.

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