MutS controls the action of DNA Polymerase IV

MARGARA LUCÍA M; ARGARAÑA CARLOS E; MONTI MARIELA R

Puerto Varas

Congreso; XII PABMB Congress; 2013

MutS contributes to the DNA replication fidelity by recognizing mispairs and recruiting factors involved in the Mismatch Repair (MMR). Interaction of MutS with the replication processivity factor β clamp has been proposed to target MutS to areas of active DNA replication to initiate MMR. We demonstrated that the MutS-b clamp interaction does not play a role in the MMR of Pseudomonas aeruginosa by characterizing a strain (mutSβ) which encodes a MutS mutant that does not interact with β clamp. Although the mutSb strain exhibits mutation rates similar to that of the parental strain, it shows a change in the mutation spectrum which is compatible with the activity of the low fidelity DNA polymerase IV (PolIV). We propose that MutS could be limiting the action of PolIV by its interaction with ß clamp. To test this hypothesis, we first analyzed the mutation spectrum in PolIV deficient strains. This assay confirmed that PolIV is responsible for the change of the mutation spectrum in the mutSβ strain. Then, we examined the effect of increasing PolIV expression levels on mutagenesis. Mutation rates were increased and PolIV-associated mutations were dominant in the mutation spectrum of the mutSβ strain. This effect depended of the catalytic activity and interaction with β clamp as overexpression of PolIV-D8A and PolIV-Δ5 mutants did not increase mutation rates, respectively. Conversely, mutagenesis was slightly promoted by PolIV in the parental strain.