A mutant of Escherichia coli hyper-resistant to a number of DNA damaging agents: Location of the mutational site

A mutant of Escherichia coli, isolated as hyper-resistant to UVC, is found to be hyper-resistant to WA, H2O2, low concentrations of nalidixic acid, novobiocin, UVA plus H2O2 and WA plus 8-methoxypsoralen. A mutational site (uvh) conferring the hyper-resistance phenotype to UVC, and presumably to other DNA damaging agents, has been mapped at the 89.9 min region on the chromosome. Complementation analysis with an F-prime uvh(+)/uvh(-) diploid strain showed that the uvh(+) allele is dominant over uvh(-) in trans. Studies with a variety of plasmids, carrying various LexA regions, introduced into the UV hyper-resistant strain show that mutation at the uvh locus may be responsible for derepression of the SOS inducible repair system. Based on the results, it is suggested that the uvh is a part of the SOS inducible system. A plausible explanation for the hyper-resistance phenotypes for various DNA damaging agents and a model for the genetic control of a second set of putative SOS regulons are presented.