Kinetics of repair of O6-methylguanine in DNA by O6-methylguanine-DNA methyltransferase in, vitro and in, vivo

David Scicchitano, Anthony E. Pegg

Research output: Contribution to journalArticlepeer-review


The demethylation of O6-methylguanine in double stranded DNA catalyzed by rat liver O6-methylguanine-DNA transmethylase was found to proceed much more rapidly when the DNA substrate was methylated to a high extent. When the content of O6-methylguanine in DNA was equal to 1 in 2000 guanines, the reaction was 90% complete within 2 min, but when the content was 1 in 500,000 it required 27 min at 37°C. These results suggest that the repair protein either moves along the DNA substrate or else has little selectivity for binding specifically to the sites containing O6-methylguanine rather than to the normal DNA. The repair of O6-methylguanine in rat liver in, vivo occurred at rates comparable to those seen in, vitro with the substrates alkylated to low extents and was virtually complete within 3 hours. These results provide strong evidence that this protein is the factor responsible for O6-methylguanine removal in, vivo and explain the wide variation in time courses reported in the literature since substrates methylated to greatly different extents have been used for such experiments.

Original languageEnglish (US)
Pages (from-to)995-1001
Number of pages7
JournalBiochemical and Biophysical Research Communications
Issue number3
StatePublished - Dec 15 1982

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology


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