Isolation of mutants sensitive to 2-aminopurine and alkylating agents and evidence for the role of DNA methylation in Penicillium chrysogenum.

Using high performance liquid chromatography, the presence of N6-methyladenine has been found at a level of 0.1 mol percent in DNA extracted from Penicillium chrysogenum. No 5-methylcytosine was detected. A mutant strain HP547, which is sensitive to the lethal effects of N-methyl-N'-nitro-N-nitrosoguanidine, methylmethane sulphonate and the base analogue 2-aminopurine shows an increased spontaneous mutation rate and no detectable DNA methylation. Comparison of restriction enzyme digests of wild type and undermethylated strains indicated that methylation was occurring at a different sequence to that of the Dam methylase system of E. coli.