Studies of aromatic biosynthetic and catabolic enzymes inUstilago maydisand in mutants ofU. violacea

Abstract

SUMMARYA multienzyme complex for five of the enzymes in the prechorismate portion of the aromatic biosynthetic pathway has been demonstrated inUstilago violacea, and has previously been reported inU. maydis(Ahmed & Giles, 1969). This complex is similar to that found inNeurospora crassaand other fungi. InU. violaceapolyaromatic-requiring mutants show pleiotropic deficiencies for all five of these enzymes, similar to the extreme pleiotropic polar mutants of thearomgene cluster in Neurospora (Giles, Case, Partridge & Ahmed, 1967a; Case & Giles, 1971). This result is interpreted as mutational evidence for anaromgene cluster inU. violaceacomparable to that inN. crassa. A second low molecular weight, heat-stable isozyme of dehydroquinase is shown to be present at high (constitutive) levels inU. 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. violaceastrains do not grow on quinate, have a single, heat-labile dehydroquinase species, and lack activities for other enzymes in the quinate catabolic pathway.