Regulation and functions of Escherichia coli genes induced by DNA damage.

Abstract

We have used the operon fusion vector Mud(Ap, lac) to generate a set of fusions within the Escherichia coli chromosome in which β- galactosidase (the product of the lacZ gene carried by the phage) is induced in response to DNA damaging agents such as UV, mitomycin C, 4-nitroquinoline-l-oxide, and N-methyl-N’-nitro-N-nitrosoguani- dine. This induction is not seen in recA - or lexA - cells. We have identified two members of this set of inducible genes as being uvrA and uvrB; the products of these two genes are required for excision repair of pyrimidine dimers and other lesions. In addition we have recently isolated a Mud(Ap, lac) insertion in the umuC gene. The product of this gene is specifically required for most chemical mutagenesis in E. coli and for inducible (Weigle) reactivation of UV- irradiated bacteriophage λ. Expression of β -galactosidase in the umuC::Mud(Ap, lac) fusion strain was induced by UV and a variety of agents in a recA + lexA +-dependent fashion. In all, the expression of ten E. coli genes is now known to be induced by DNA damage. Genetic analysis and biochemical experiments indicate that the lexA gene product is the direct repressor of these genes and that proteolytic cleavage of the lexA protein by the recA protease is required for their induction.