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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 a putative operon comprising Rv3395c, which encodes a protein of unknown function restricted primarily to actinomycetes, and Rv3394c, which is predicted to encode a Y-family DNA polymerase. These genes were previously identified as components of an imuA-imuB-dnaE2–type mutagenic cassette widespread among bacterial genomes. Here, we confirm that Rv3395c (designated imuA′) and Rv3394c (imuB) are individually essential for induced mutagenesis and damage tolerance. Yeast two-hybrid analyses indicate that ImuB interacts with both ImuA′ and DnaE2, as well as with the β-clamp. Moreover, disruption of the ImuB-β clamp interaction significantly reduces induced mutagenesis and damage tolerance, phenocopying imuA …