reactions specifically involved in tryptophan biosynthesis are under the T?ntrol of four genes in Neurospora crassa (AHMAD and CATCHESIDE 1960). The complexity of the gene-enzyme relationships in this pathway was discovered by AHMAD and CATCHESIDE (1960) and AHMAD, KHALIL, KHAN and MOZMADAR (1964) who demonstrated that lesions at one of these genes, tryp-2, could prevent either the accumulation...