A novel inducible mutagenesis system in Mycobacterium tuberculosis

Abstract

In Mycobacterium tuberculosis (Mtb), damage‐induced mutagenesis is dependent on the C‐family DNA polymerase, DnaE2. Included with dnaE2 in the Mtb SOS regulon is an operon comprising Rv3395c, which encodes a protein of unknown function, and Rv3394c, which is predicted to encode a Y‐family DNA polymerase. Our results show that Rv3395c (designated imuA′) and Rv3394c (imuB) are individually essential for induced mutagenesis and damage tolerance and that ImuB interacts with both ImuA′ and DnaE2, as well as with the β‐clamp. Disruption of the ImuB‐β clamp interaction significantly reduces induced mutagenesis and damage tolerance, phenocopying deletion mutants in imuA′, imuB, and dnaE2. Despite retaining structural features characteristic of Y‐family members, ImuB homologs are pseudo‐polymerases which lack conserved active‐site residues. In contrast, mutation of catalytic, aspartate residues in DnaE2 reproduces the dnaE2 gene deletion phenotype, implicating this polymerase in mutagenic lesion bypass. Together, these results identify the split imuA′‐imuB/dnaE2 cassette as a compelling target for compounds designed to limit mutagenesis in a pathogen increasingly associated with drug resistance