Interestingly, we observe that recA has the highest d N / d S score of all the genes in Mtb on the branch leading to the Mtb complex, and recB also has a very high score. Mycobacteria lack a mutSL-based mismatch repair (MMR) system [42] , and it is believed that recA may be involved in compensating pathways. dnaE2 (DNA polymerase III) also has one of the highest d N /d S values on the branch leading to Mtb, and both dnaE1 (DNA polymerase III) and dnaE2 show evidence of selection on the branch leading to the pathogenic Mycobacteria. In Mtb, damage-induced base-substitution mutagenesis is dependent on dnaE2. Loss of dnaE2 activity renders Mtb hypersensitive to DNA damage, eliminates induced mutagenesis, attenuates virulence, and reduces the frequency of drug resistance in vivo [39, 45] . dnaE1 provides essential, high-fidelity replicative polymerase function [39] , and is expressed in response to DNA damage, along with dnaE2 and recA [39, 45] .