Cellular reactions of O6-methylguanine, a product of some alkylating carcinogens.

Cultures of a purine-requiring mutant of Chinese hamster ovary cells (CHO-104b), randomly bred hamster embryo cells, or Escherichia coli B(s-1) were treated with non-toxic doses of (3)H-labelled O(6)-methylguanine. DNA and RNA were isolated and subjected to enzymic digestion to nucleosides at pH8. The products of digestion were analysed by ion-exchange chromatography on columns of Dowex 50 (NH(4) (+) form) at pH8.9. No (3)H-labelled O(6)-methylguanosine was detected in nucleic acid digests. (3)H-labelled O(6)-methylguanine was O-demethylated yielding [(3)H]guanine in CHO-104b cells. Radioactivity in nucleic acid digests was associated with thymidine, guanosine, deoxyguanosine and an unidentified early-eluting product. Reports of similar unidentified products from nucleic acids labelled with various agents are discussed.