Effects of modulation of RNase H production on the recovery of DNA synthesis following UV-irradiation in Escherichia coli.

The requirements for the recovery of DNA synthesis in UV-irradiated Escherichia coli were analysed in strains having varied levels of RNase H and RecA protein. We have previously shown (Khidhir et al. 1985) that the recovery of DNA synthesis in E. coli following UV treatment is an inducible SOS function requiring protein synthesis. We proposed that this reflected the need for the synthesis of specific induced replisome reactivation factor(s) for recovery. In this study we now show that recovery of DNA synthesis can in fact take place in the absence of protein synthesis in a mutant lacking RNase H and having high (constitutive) levels of RecA protein. We also show that expression of rnh is inhibited during the SOS response in recA+ but not in a recA- strain. The results are discussed in relation to the mechanism of recovery of DNA synthesis following UV irradiation in E. coli.