Phylogenetic tree of Actinomycetales YrbE proteins. A non-redundant set of YrbE protein sequences were aligned and an unrooted neighbor-joining tree was computed by MEGA. Coloring corresponds to the classification scheme specified in Table 3. ORFs are designated by [gene locus name | operon number (1–8) and gene position (A, B)]. Where operon orthology cannot be inferred, operons are designated: -1, -2.