The SMC-Like Protein Complex SbcCD Enhances DNA Polymerase IV-Dependent Spontaneous Mutation in Escherichia coli

In Escherichia coli, RpoS, the general stress response sigma factor, regulates the activity of the specialized DNA polymerase DNA polymerase IV (Pol IV) both in stationary-phase and in exponential-phase cells. Because during exponential phase dinB, the gene encoding Pol IV, is transcribed independently of RpoS, RpoS must regulate Pol IV activity in growing cells indirectly via one or more intermediate factors. The results presented here show that one of these intermediate factors is SbcCD, an SMC-like protein and an ATP-dependent nuclease. By initiating or participating in double-strand break repair, SbcCD may provide DNA substrates for Pol IV polymerase activity. In Escherichia coli and its relatives, DNA damage results in the induction of about 40 genes as part of the SOS response. Three of these genes encode specialized DNA polymerases: DNA polymerase II (Pol II; encoded by the polB gene), DNA Pol IV (encoded by the dinB gene), and DNA Pol V (encoded by the umuDC genes) (11, 35). Pol IV and Pol V are members of the Y family of DNA polymerases that are widely distrib-uted in all domains of life. Y family polymerases can replicat