Repair of O6-methylguanine, by mammalian cell extracts, in alkylated DNA and poly(dG-m5dC).(poly dG-m5dC) in B and Z forms.

The ability of rat hepatoma cells extracts to repair O6-methylguanine was measured using as substrate alkylated DNA and alkylated poly(dG-m5dC).poly(dG-m5dC) either in the B or in the Z conformation. The O6-methylguanine-DNA methyltransferase had similar activities on DNA and on the right-handed polymer. However, when the polymer was in the Z conformation, the protein activity represented approximately 10% of that measured on DNA. Therefore the efficiency of O6-methylguanine repair is related to the DNA conformation and is markedly reduced during the B to Z transition of the substrate.