^agi numbers in boldface type refer to the seven protein domains that function in primary Trp biosynthesis and that were used to construct the tree shown in Fig. 2. Entries under the HisA column are restricted to actinomycete bacteria, which lack a native TrpC and where HisA is uniquely competent for both TrpC and HisA isomerase functions (denoted PriA). Abbreviation: N/A, not available. Superscripts: ^P indicates a paralog; ^R indicates a remnant; ^S indicates presence of a pseudogene due to frameshift; ^X indicates a xenolog. In cases where identity as a paralog or xenolog is uncertain, provisional designation as a paralog is deemed the most conservative. Two identical gene identification (gi) numbers with N-terminal and C-terminal bullets (•) refer to catalytic domains encoded by genes that are fused. ^bThe 47 organisms used in Fig. 2 are denoted in boldface type. Organisms are named according to designations used in the GOLD database. In many cases (e.g., Escherichia, Salmonella, and Helicobacter) only one genome among closely related organisms has been listed because they are very similar. ^cTCG stands for "Tryptophan Cohesion Groups" (see Table 3 for details). ^dPriA is that subsection of HisA homologs that are able to carry out the TrpC isomerase function as well as the HisA isomerase function. ^eThe three TrpD paralogs from Anabaena sp. (from top to bottom) were referred to as TrpD_2, TrpD_1, and TrpD_3 in Xie et al. [7]. ^fTrpAb in TCG-6 organisms is a dual-function amidotransferase that also functions in p-aminobenzoate biosynthesis. It is located in the pab operon.