ImuA participates in SOS mutagenesis by interacting with RecA1 and ImuB in Myxococcus xanthus

Bacteria have two pathways to restart stalled replication forks caused by environmental stresses, error-prone translesion DNA synthesis (TLS) catalyzed by TLS polymerase and error-free template switching catalyzed by RecA, and their competition on the arrested fork affects bacterial SOS mutagenesis. DnaE2 is an error-prone TLS polymerase, and its functions require ImuA and ImuB. Here we investigated the function of imuA, imuB and dnaE2 in Myxococcus xanthus and found that imuA showed differences from imuB and dnaE2 in bacterial growth, resistance and mutation frequency. Transcriptomics analysis found that ImuA were associated with bacterial SOS response. Yeast-two-hybrid scanning revealed that ImuA interacted with RecA1 besides ImuB. Protein activity analysis proved that ImuA had no DNA binding activity, but inhibited the DNA binding and recombinase activity of RecA1. These findings highlight that ImuA not only participates in TLS by binding ImuB, but also inhibits the recombinase activity of RecA1 in M. xanthus, suggesting a role of ImuA in the two replication restart pathways. ImportanceDnaE2 is responsible for bacterial SOS mutagenesis in nearly one third of sequenced bacterial strains. However, its mechanism, especially the function of its accessory protein ImuA, is still unclear. Here we reported that M. xanthus ImuA might facilitate DnaE2 TLS by inhibiting the recombinase activity of RecA1, which helps to explain the mechanism of DnaE2-dependent TLS and the scientific problem of choosing one of the two restart pathways to repair the stalled replication fork.