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 language||English (US)|
|Number of pages||7|
|Journal||Biochemical and Biophysical Research Communications|
|State||Published - Dec 15 1982|
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology