Effect of an umuC mutation on phage lambda induction.

A possible role of the umuC gene product in the induction of the SOS responses was examined. We compared the expression of a genetic fusion, in which gene lacZ, encoding beta-galactosidase in Escherichia coli is under the direct control of the cI repressor from prophage lambda, in a umuC+ strain and in an otherwise isogenic umuC- mutant. We found that two times higher UV doses were required to obtain a similar induction in the umuC+ strain as in the umuC mutant. In addition we showed that, at the same UV dose after a lag period, the specific activity of beta-galactosidase increased more rapidly in the umuC mutant. We suggest that the wild-type umuC gene product participates in the processing of the SOS inducing structures caused by UV irradiation or prevents formation of some of them. This is compatible with a role of the UmuC protein in DNA synthesis past a replication block.