Induction of umu gene expression by cross-links and other DNA lesions

The induction of umu gene expression by DNA cross-links was investigated in various strains of E. coli with different DNA-repair capacities. Expression was measured by quantifying enzymatic activity of beta-galactosidase produced under regulation of the umu promoter carried on a plasmid carrying the umuC-lacZ gene fusion. The treatment with MMC induced gene expression more efficiently in a wild-type strain when compared with an excision-repair-deficient strain (uvrA). In contrast, PUVA and cis-Pt treatment induced higher levels of the gene expression in the uvrA strain than in the wild-type strain, as did other DNA-damaging agents including 4NQO, MNNG and MMS. None of these chemicals induced umu expression in either lexA and recA strains. The mechanisms of the induction of umu expression by DNA cross-links in relation to DNA damage and repair are discussed.