Interaction between the DNA replication and repair processes in bacteria

Seattle

Exposición; Seminario del Departamento de Microbiología de la Universidad de Washington; 2017

We report that MutS regulates the access of the low fidelity DNA Polymerase (Pol) IV to replication through its interaction with the processivity factor β clamp in Pseudomonas aeruginosa. Based on in vitro assays, we found that MutS inhibits the association of Pol IV with β clamp, which is absolutely required for the activity of this Pol. Conversely, MutSβ, a mutant version that fails to bind β clamp, was not able to prevent Pol IV-β clamp interaction. These data suggested that MutS and Pol IV may compete for binding to β clamp. To analyze the relevance of this competition in vivo, we evaluated the effect of Pol IV overexpression on mutagenesis of diverse chromosomal genes in a mutant strain harboring a chromosomal mutSβ allele compared to the parental strain. Pol IV overexpression increased ~10-fold mutation rates at all Pol IV expression levels tested in the parental strain, indicating that the Pol IV mutagenic activity is controlled in these cells. This control was not evidenced in the mutSβ strain since it showed a concomitant increase of mutation rates with Pol IV levels reaching a maximum of ~45-fold. Finally, analysis of mutation spectra revealed that Pol IV strongly contributes to spontaneous mutations in the mutSβ strain whereas it has a lesser impact on mutagenesis in the parental strain. This work reveals a novel mechanism by which MutS maintain replication fidelity.