Structure and expression of the alkA gene of Escherichia coli involved in adaptive response to alkylating agents

Nucleotide sequence of a DNA fragment containing the alkA gene and its control region has been determined using a chemical method. Only one open reading frame responsible for 3-methyladenine DNA glycosylase II was found. The hypothetical polypeptide deduced from the DNA sequence, with a molecular weight of 31,400, had an amino-terminal sequence and total amino acid composition identical to that of purified 4-methyladenine DNA glycosylase II. We constructed hybrid plasmids carrying an alkA'-lacZ' fusion, with the proper control region for alkA expression. A hybrid polypeptide with β-galactosidase activity was formed when lac mutant cells harboring such plasmids were incubated with low doses of N-methyl-N'-nitro-N'-nitrosoguanidine or methylmethane sulfonate. Other DNA-damaging agents, such as ethylmethane sulfonate, nalidixic acid, and ultraviolet light did not induce the enzyme activity. The induction was controlled by the ada and adc, but not by the recA and lexA genes.