Stimulation of transfer of methyl groups from O6-methylguanine in DNA to protein by rat liver extracts in response to hepatotoxins.

An enzymatic activity present in rat liver extracts catalyzes the transfer of methyl groups from O6-methylguanine in DNA to protein. This activity was stimulated by treatment of rats with thioacetamide, carbon tetrachloride, 1,2-dimethylhydrazine, diethylnitrosamine, dimethylnitrosamine and by partial hepatectomy but not by treatment with N-methyl-N-nitrosourea or streptozotocin. These results suggest that an enhancement of this activity accompanies the increase in cell division brought about by these agents and is not necessarily a specific response to the presence of alkylated bases in DNA.