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

Abstract

Cultures of a purine-requiring mutant of Chinese hamster ovary cells (CHO-104b), randomly bred hamster embryo cells, or Escherichia coli Bs-1 were treated with non-toxic doses of 3H-labelled O6-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 (NH4+ form) at pH8.9. No 3H-labelled O6-methylguanosine was detected in nucleic acid digests. 3H-labelled O6-methylguanine was O-demethylated yielding [3H]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.