Binding of MutS protein to oligonucleotides containing a methylated or an ethylated guanine residue, and correlation with mutation frequency

Kentaro Taira, Shintaro Nakamura, Khota Nakano, Daisuke Maehara, Keinosuke Okamoto, Sakae Arimoto, David Loakes, Leroy Worth, Roel M. Schaaper, Kohji Seio, Mitsuo Sekine, Kazuo Negishi, Tomoe Negishi

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


The MutS-based mismatch repair (MMR) system has been conserved from prokaryotes to humans, and plays important roles in maintaining the high fidelity of genomic DNA. MutS protein recognizes several different types of modified base pairs, including methylated guanine-containing base pairs. Here, we looked at the relationship between recognition and the effects of methylating versus ethylating agents on mutagenesis, using a MutS-deficient strain of E. coli. We find that while methylating agents induce mutations more effectively in a MutS-deficient strain than in wild-type, this genetic background does not affect mutagenicity by ethylating agents. Thus, the role of E. coli MMR with methylation-induced mutagenesis appears to be greater than ethylation-induced mutagenesis. To further understand this difference an early step of repair was examined with these alkylating agents. A comparison of binding affinities of MutS with O6-alkylated guanine base paired with thymine, which could lead to transition mutations, versus cytosine which could not, was tested. Moreover, we compared binding of MutS to oligoduplexes containing different base pairs; namely, O6-MeG:T, O6-MeG:C, O6-EtG:T, O6-EtG:C, G:T and G:C. Dissociation constants (Kd), which reflect the strength of binding, followed the order G:T- > O6-MeG:T- > O6-EtG:T- = O6-EtG:C- ≥ O6-MeG:C- > G:C. These results suggest that a thymine base paired with O6-methyl guanine is specifically recognized by MutS and therefore should be removed more efficiently than a thymine opposite O6-ethylated guanine. Taken together, the data suggest that in E. coli, the MMR system plays a more significant role in repair of methylation-induced lesions than those caused by ethylation.

Original languageEnglish
Pages (from-to)107-112
Number of pages6
JournalMutation Research - Fundamental and Molecular Mechanisms of Mutagenesis
Issue number1-2
Publication statusPublished - Apr 2 2008
Externally publishedYes


  • Mismatch repair
  • MutS
  • Mutation
  • O-ethylguanine
  • O-methylguanine

ASJC Scopus subject areas

  • Molecular Biology
  • Genetics
  • Health, Toxicology and Mutagenesis


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