Comparative gene expression profiles following UV exposure in wild-type and SOS-deficient Escherichia coli

The SOS response in W-irradiated Escherichia coli includes the upregulation of several dozen genes that are negatively regulated by the LexA repressor . Using DNA microarrays containing amplified DNA fragments from 95.5% of al l open reading frames identified on the E. coli chromosome, we have examine d the changes in gene expression following UV exposure in both wild-type ce lls and lexA1 mutants, which are unable to induce genes under LexA control. We report here the rime courses of expression of che genes surrounding the 26 documented lexA-regulated regions on the E. coli chromosome. We observe d 17 additional sites that responded in a lexA-dependent manner and a large number of genes that were upregulated in a lexA-independent manner althoug h upregulation in this manner was generally not more than twofold. in addit ion, several transcripts were either downregulated or degraded following UV irradiation. These newly identified W-responsive genes are discussed with respect to their possible roles in cellular recovery following exposure to W irradiation.