Genetic analyses of cellular functions required for UV mutagenesis in Escherichia coli

In Escherichia coli, most UV and chemical mutagenesis is not a passive process and requires the participation of the umuD and umuC gene products. However, the molecular mechanism of UV mutagenesis is not yet understood and the roles of the UmuD and UmuC proteins have not been elucidated. The umuDC operon is induced by UV irradiation and regulated as part of the SOS response. Genetic evidence now indicates that RecA-mediated cleavage activates UmuD for its role in mutagenesis. The COOH-terminal fragment of UmuD is both necessary and sufficient for this role. The RecA protein appears to have a third role in UV mutagenesis besides mediating the cleavage of LexA and UmuD at the time of SOS induction. In addition, we have obtained evidence which indicates that the GroEL and GroES proteins also play a role in UV mutagenesis. Similarities of the amino acid sequence of UmuD to the sequence of gene 45 protein of bacteriophage T4 and of the sequence of UmuC to those of the gene 44 and gene 62 proteins suggest possible roles for UmuD and UmuC in mutagenesis that are supported by preliminary evidence.