SbmC limits the mutation rate of Escherichia coli

Both mutagenic and non-mutagenic DNA damage repair is coordinated by the SOS response, but despite extensive work, the functions of some SOS-induced genes remain obscure. Here, we clarify the function of Escherichia coli SbmC (GyrI).

Despite its proposed function as a gyrase inhibitor, cells either lacking or overexpressing SbmC instead exhibit phenotypes consistent with a role in limiting DNA damage and cellular variation. Importantly, SbmC levels inversely correlate with E. coli mutation rate. Excess SbmC limits mutation whereas loss of SbmC increases mutation, possibly because ∆sbmC cells variably induce the SOS response, including mutagenic DNA Pol V. We additionally show that SbmC is dispensable for survival in the presence of double-strand break inducing drugs but is required to limit their mutational effects.