FIG. 21. Quinate (aromatic amino acid) catabolic pathway, showing sites of gene action (146, 148, 387, 423, 517, and references therein). qa-1 is a regulatory gene affecting all three structural genes. qa-2+ activity (catabolic dehydroquinase) can be replaced by the product of aro-9+, the equivalent gene in the aromatic biosynthetic pathway. See reference 423 for the catabolic steps subsequent to protocatechuic acid.