A Possible Regulatory Gene for the Molybdenum-Containing Cofactor in Aspergillus nidulans

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Abstract
A. nidulans has 3 molybdoenzymes, nitrate reductase, purine hydroxylase I and purine hydroxylase II. These 3 enzymes share a Mo-containing cofactor whose synthesis requires the integrity of 5 loci, designated cnxABC, cnxE, cnxF, cnxG and cnxH. The existence of a 6th locus, designated cnxJ, which might be involved in the regulation of cofactor levels is reported. 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.degree. C (but not 25.degree. C) shows some similarities to that of the 2 cnxJ- alleles. A structural role for the cnxC (or cnxABC) product in the cofactor is tentatively suggested.