A DNA methyltransferase can protect the genome from postdisturbance attack by a restriction-modification gene complex

Noriko Takahashi, Yasuhiro Naito, Naofumi Handa, Ichizo Kobayashi

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59 Citations (Scopus)


In prokaryotic genomes, some DNA methyltransferases form a restriction-modification gene complex, but some others are present by themselves. Dcm gene product, one of these orphan methyltransferases found in Escherichia coli and related bacteria, methylates DNA to generate 5′-CmCWGG just as some of its eukaryotic homologues do. Vsr mismatch repair function of an adjacent gene prevents C-to-T mutagenesis enhanced by this methylation but promotes other types of mutation and likely has affected genome evolution. The reason for the existence of the dcm-vsr gene pair has been unclear. Earlier we found that several restriction-modification gene complexes behave selfishly in that their loss from a cell leads to cell killing through restriction attack on the genome. There is also increasing evidence for their potential mobility. EcoRII restriction-modification gene complex recognizes the same sequence as Dcm, and its methyltransferase is phylogenetically related to Dcm. In the present work, we found that stabilization of maintenance of a plasmid by linkage of EcoRII gene complex, likely through postsegregational cell killing, is diminished by dcm function. Disturbance of EcoRII restriction-modification gene complex led to extensive chromosome degradation and severe loss of cell viability. This cell killing was partially suppressed by chromosomal dcm and completely abolished by dcm expressed from a plasmid. Dcm, therefore, can play the role of a "molecular vaccine" by defending the genome against parasitism by a restriction-modification gene complex.

Original languageEnglish
Pages (from-to)6100-6108
Number of pages9
JournalJournal of Bacteriology
Issue number22
Publication statusPublished - 2002 Nov

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology


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