Dispersal and regulation of an adaptive mutagenesis cassette in the bacteria domain

Recently, a multiple gene cassette with mutagenic translation synthesis activity was identified and shown to be under LexA regulation in several proteobacteria species. In this work, we have traced down instances of this multiple gene cassette across the bacteria domain. Phylogenetic analyses show that this cassette has undergone several reorganizations since its inception in the actinobacteria, and that it has dispersed across the bacterial domain through a combination of vertical inheritance, lateral gene transfer and duplication. In addition, our analyses show that LexA regulation of this multiple gene cassette is persistent in all the phyla in which it has been detected, and suggest that this regulation is prompted by the combined activity of two of its constituent genes: a polymerase V homolog and an alpha subunit of the DNA polymerase III.