The open reading frame TTC1157 of Thermus thermophilus HB27 encodes the methyltransferase forming N2-methylguanosine at position 6 in tRNA

  1. Louis Droogmans6,7
  1. 1Institut de Recherches Microbiologiques Jean-Marie Wiame, B-1070 Bruxelles, Belgium
  2. 2Structural Biology Brussels, Vrije Universiteit Brussel, 1050 Brussels, Belgium
  3. 3VIB Department of Structural Biology, 1050 Brussels, Belgium
  4. 4International Institute of Molecular and Cell Biology in Warsaw, PL-02-109 Warsaw, Poland
  5. 5Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, PL-61-614 Poznan, Poland
  6. 6Laboratoire de Microbiologie, Université Libre de Bruxelles (ULB), B-1070 Bruxelles, Belgium

    Abstract

    N2-methylguanosine (m2G) is found at position 6 in the acceptor stem of Thermus thermophilus tRNAPhe. In this article, we describe the cloning, expression, and characterization of the T. thermophilus HB27 methyltransferase (MTase) encoded by the TTC1157 open reading frame that catalyzes the formation of this modified nucleoside. S-adenosyl-L-methionine is used as donor of the methyl group. The enzyme behaves as a monomer in solution. It contains an N-terminal THUMP domain predicted to bind RNA and contains a C-terminal Rossmann-fold methyltransferase (RFM) domain predicted to be responsible for catalysis. We propose to rename the TTC1157 gene trmN and the corresponding protein TrmN, according to the bacterial nomenclature of tRNA methyltransferases. Inactivation of the trmN gene in the T. thermophilus HB27 chromosome led to a total absence of m2G in tRNA but did not affect cell growth or the formation of other modified nucleosides in tRNAPhe. Archaeal homologs of TrmN were identified and characterized. These proteins catalyze the same reaction as TrmN from T. thermophilus. Individual THUMP and RFM domains of PF1002 from Pyrococcus furiosus were produced. These separate domains were inactive and did not bind tRNA, reinforcing the idea that the THUMP domain acts in concert with the catalytic domain to target a particular position of the tRNA molecule.

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    Footnotes

    • Received September 19, 2011.
    • Accepted December 22, 2011.
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