RELEASE OF N2,3-ETHANOGUANINE FROM HALOETHYLNITROSOUREA-TREATED DNA BY ESCHERICHIA-COLI 3-METHYLADENINE DNA GLYCOSYLASE-II

3-Methyladenine DNA glycosylase II (Gly II), purified from Escherichia coli cells which carry the plasmid PYN1000, has been tested for its ability to release N2,3-ethanoguanine from DNA modified by the antitumor agent N-[2-chloroethyl-1,2-C-14]-N'-cyclohexyl-N-nitrosourea [C-14]CCNU. Gly II has been shown to release N2,3-ethanoguanine in a protein- and time-dependent manner at a rate that exceeds the rate at which this enzyme releases other alkylated bases from [C-14]CCNU-modified DNA. This finding widens the known substrate specificity for Gly II to include a modified base which bears an exocyclic ring structure, a class of modifications caused by a variety of chemical carcinogens.