Abstract
Cell extracts from Micrococcus luteus release both free 3-methyladenine and free 7-methylguanine from alkylated DNA. The glycosylase activity responsible for the liberation of 7-methylguanine is not 3-methyladenine-DNA glycosylase, which, when purified, does not liberate it. Furthermore, the heat inactivation rates of the two enzymatic activities are different. The release of 7-methylguanine by chemical depurination of ethanol-soluble oligonucleotides has been ruled out. A similar activity releasing 7-methylguanine is also found in Escherichia coli.