The mycobacterial mutasome - comprising ImuA', ImuB, and DnaE2 - has been implicated in DNA damage-induced mutagenesis in Mycobacterium tuberculosis. ImuB, which is predicted to enable mutasome function via its interaction with the β clamp, is a catalytically inactive Y-family DNA polymerase. Like some other members of the Y-family, ImuB features a recently identified amino acid motif with homology to the RecA N-terminus (RecA-NT). Given the role of RecA-NT in RecA oligomerization, we hypothesized that ImuB RecA-NT mediates the interaction with ImuA', a RecA homolog of unknown function. Here, we constructed a panel of imuB alleles in which the RecA-NT was removed, or mutated. Our results indicate that RecA-NT is critical for the interaction of ImuB with ImuA'. A region downstream of RecA-NT, ImuB-C, appears to stabilize the ImuB-ImuA' interaction, but its removal does not prevent complex formation. In contrast, replacing two hydrophobic residues of RecA-NT, L378 and V383, disrupts the ImuA'-ImuB interaction. To our knowledge, this is the first experimental evidence suggesting a role for RecA-NT in mediating the interaction between a Y-family member and a RecA homolog.
Keywords: DNA repair; Mycobacterium tuberculosis; antibiotic resistance; mutagenesis; mutasome; protein-protein interaction.
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