FIG. 11. Biosynthetic pathways of the aromatic amino acids, showing sites of action to the aro, trp, pt, phe, tyr, and T genes (98, 147, 201, 259, 316, 387, 437, 473, 519, 546, 1126, 1167). The conversion of chorismate to p-aminobenzoate has not been demonstrated in Neurospora. In the conversion of tyrosine to melanin, the later steps are nonenzymatic. The gene products of trp-1 and trp-2 form an enzyme aggregate with three properties; a given trp-1 mutation may block one or more of the reactions. aro-9+ activity (biosynthetic dehydroquinase) can be replaced by the product of qa-2+, the equivalent gene in the catabolic pathway (885). Pretyrosine accumulates when other pathways are blocked (see phe-2). PRPP, 5-Phosphoribosyl pyrophosphate.