NITRATE REDUCTASE OF THE ASCOMYCETOUS FUNGUS, LEPTOSPHAERIA-MACULANS - GENE SEQUENCE AND CHROMOSOMAL LOCATION

The nitrate reductase (niaD) gene was isolated from the phytopathogeni c loculoascomycete Leptosphaeria maculans by screening a genomic DNA l ibrary with the Aspergillus nidulans niaD gene. The L. maculans niaD g ene is the first protein-encoding gene characterised from this fungus. It encodes a predicted protein of 893 amino acids and contains four p utative introns at positions in the gene equivalent to those of four o f the six introns in the A. nidulans niaD gene. Mutants defective in n iaD and molybdenum cofactor gene(s) of L. maculans have been isolated. Transformation of a L. maculans niaD mutant with a 3.8 kb SacII fragm ent containing the L. maculans niaD gene restored wild-type growth on nitrate as a sole nitrogen source. The niaD gene is present as a singl e copy on a chromosome which ranges in size from 2.6 to 2.8 Mb between the different L. maculans isolates examined.