DNA damage to E. coli elicits a response (the SOS response) which results in the derepression of at least 13 different genes or operons. One of these operons, the umuC operon produces two proteins which are required for the expression of induced mutagenesis. Current hypotheses state that the mutagenesis resulting from the derepression of the umuC operon performs a DNA repair function which allows DNA polymerae to by-pass UV lesions in DNA templates. UV damaged single-stranded DNA phage, such as 0X174, can be reactivated by UV treatment of the host. The hypothetical umuC dependent DNA repair system has been proported to be responsible for this induced reactivation and mutagenesis of 0X174.