We also observe positive selection for dinX (DNA polymerase IV) on the branch leading to the pathogenic Mycobacteria (branch-site model) in our d N /d S analysis (see Supplementary Information website). Most organisms use specialized DNA polymerases that are able to catalyze translesion synthesis (TLS) across sites of damage, including the dinB group of Y family polymerases. There are two dinB-family polymerases in Mtb (dinX and dinP). Unlike in other bacteria, dinX and dinP expression are not dependent on recA, the SOS response, or the presence of DNA damage, and could therefore serve a novel yet uncharacterized role in Mtb [46] [47] [48] [49] .