Phylogenetic tree of TrpAb sequences. Xfa_2 is a probable specialized-pathway xenolog from Xylella. Sco_CDA is a specialized-pathway paralog within TCG-5. TCG-1 contains a xenolog (PhnB) from Pseudomonas aeruginosa that (together with PhnA) is encoded by genes of a partial-pathway operon. Trp Ab genes from Helicobacter pylori, Corynebacterium diptheriae, and C. glutamicum are xenolog members of whole-pathway operons. TCG-2 and TCG-7 are fragmented. (Consult Fig. 2 for intact TCGs.) Asterisks (Tma, Cje, and Eco) indicate domains that exist as part of TrpAb•TrpB fusions.