METHYL METHANESULFONATE MUTAGENESIS IN BACTERIOPHAGE T4

John W. Drake ¹

¹ Laboratory of Genetics, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709

MMS induces diverse rII mutations from a wild-type background in bacteriophage T4. About 56% are base pair substitutions, about 30% are frameshift mutations, and the remainder is a miscellaneous set of rapidly reverting or leaky mutants of unknown composition; but deletions were not detected. MMS-induced forward mutation is sharply reduced by the mutations px and y, which also reduce ultraviolet, photodynamic and -ray mutagenesis and increase killing by all of these agents. Thus, many of the mutations arise via the T4 WXY system. The induction of G:C A:T transitions was detected even in a px or y background using sensitive reversion tests, and the few forward rII mutations that were induced from this background also behaved like transition mutations. Thus, some MMS-induced mutations arise independently of the WXY system, perhaps as a result of the (rather weak) ability of MMS to alkylate the O⁶ position of guanine.