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

Aspergillus nidulans has three molybdoenzymes, nitrate reductase, purine hydroxylase I and purine hydroxylase II. These three enzymes share a molybdenum-containing cofactor whose synthesis requires the integrity of five loci, designated cnxABC, cnxE, cnxF, cnxG and cnxH. Here we report the existence of a sixth locus, designated cnxJ, which might be involved inthe regulation of cofactor levels. When grown in the presence, but not in the absence, of tungstate or methylammonium, strains 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 degrees C (but not 25 degrees C) shows some similarities to that of the two cnxJ- alleles. A structural role for the cnxC (or cnxABC) product in the cofactor is tentatively suggested.