Inducibility ofageneproduct required forUV andchemical mutagenesis inEscherichia coli

ABSTRACT Theproductofthe umuC gene is requiredfor UV andchemical mutagenesis in Escherichia coli. Bythe use oftheMud(Ap, lac) bacteriophage, we haveobtained an operon fusionofthe lac structural genes to the promoter/regulatory region ofthe umuCgene. The strain containing the umuC::Mud(Ap, lac)fusion was identified on thebasisof its UV nonmutability. Strains containing this putative null allele of umuCwere (i) nonmutableby UV andotheragents,(ii) slightly UV sensitive, and(iii) deficient in their ability to carry out Weigle reactivation ofUV-irradiatedbacteriophage A. The UV nonmutabilityofthe strain couldbesup-pressed by a derivative of the mutagenesis-enhancing plasmid pKMlOL. -Galactosidasesynthesis in umuC::Mud(Ap,l4c)fusion strains was inducible by UV and other DNA-damaging agents.Genetic analysis of the regulation of 8-galactosidase in umuC::Mud(Ap, lac) strains suggests that the lexA protein is thedirectrepressorofthe umuC geneandthat a functionofthe recA protein,probably its proteaseactivity,