Published online by Cambridge University Press: 14 April 2009
A multienzyme complex for five of the enzymes in the prechorismate portion of the aromatic biosynthetic pathway has been demonstrated in Ustilago violacea, and has previously been reported in U. maydis (Ahmed & Giles, 1969). This complex is similar to that found in Neurospora crassa and other fungi. In U. violacea polyaromatic-requiring mutants show pleiotropic deficiencies for all five of these enzymes, similar to the extreme pleiotropic polar mutants of the arom gene cluster in Neurospora (Giles, Case, Partridge & Ahmed, 1967a; Case & Giles, 1971). This result is interpreted as mutational evidence for an arom gene cluster in U. violacea comparable to that in N. crassa. A second low molecular weight, heat-stable isozyme of dehydroquinase is shown to be present at high (constitutive) levels in U. maydis, as previously indicated by Ahmed & Giles (1969), but this activity is increased to extraordinarily high levels in cells grown in the presence of quinate. In contrast, U. violacea strains do not grow on quinate, have a single, heat-labile dehydroquinase species, and lack activities for other enzymes in the quinate catabolic pathway.