Department of Biochemistry, Ohio State University, Columbus 43210.
The nit-3 gene of the filamentous fungus Neurospora crassa encodes the enzyme nitrate reductase, which catalyzes the first reductive step in the highly regulated nitrate assimilatory pathway. The nucleotide sequence of nit-3 was determined and translates to a protein of 982 amino acid residues with a molecular weight of approximately 108 kDa. Comparison of the deduced nit-3 protein sequence with the nitrate reductase protein sequences of other fungi and higher plants revealed that a significant amount of homology exists, particularly within the three cofactor-binding domains for molybdenum, heme and FAD. The synthesis and turnover of the nit-3 mRNA were also examined and found to occur rapidly and efficiently under changing metabolic conditions.