A possible regulatory gene for the molybdenum-containing cofactor in Aspergillus nidulans

Aspergillus nidulans has three molybdoenzvmes, nitrate reductase nitrate reductase, purine hydroxylase I and purine hydroxylase II. These three enzymes share a molybdenum-containing cofactor whose synthesis requires the inteegrity of five loci, designated cnxABC, cnxE, cnxG and cnxH. Here we report the existence of a sixth locus, designated cnxj which might be involved in the regular of cofactor levels. When grown in the presence, but not in the absence, of tungstate or methylammonium, stains carrying cnxJ1 or cnxJ2 have reduced molybdoenzyme levels as judged both from growth properties and enzyme determinations. A new cryosensitive cnxC− allele is also reported. Its phenotype at 37 °C (but not 25 °C) shows some silmiarities to that of the two cnxJ- alleles. A structural role for the cnxC (or cnxABC) product in the coafctor is tentatilvey suggested.