Multiple sequence alignment of the *AroQ protein family in relationship with the known three-dimensional structure of the AroQ domain of AroQPheA from E. coli. (The AroQ domain of AroQTyrA from E. coli is also shown.) Acronyms for organisms are as given in Table 7. The cleavable signal peptides of *AroQ proteins are shown in orange. The carboxy-terminal extensions of *AroQ proteins, which have no counterpart in other AroQ protein domains, are shown in blue. Residues located at the active site of the AroQ domain of E. coli AroQPheA as demonstrated by X-ray crystallography, are marked with arrowheads and assigned the E. coli AroQPheA residue numbers. Arrowheads marked with H are hydrophobic residues, and residue 88 is always Q or E. Conserved residues are shown in yellow. Active-site residues of AroQPheA from E. coli that are conserved in all eight *AroQ sequences are marked with an asterisk.