title: Amber nonsense mutations in regulatory and structural genes of the nitrogen control circuit of Neurospora crassa.
abstract: Neurospora crassa possesses a set of nitrogen-regulated enzymes whose expression requires a lifting of nitrogen catabolite repression and specific induction. The nit-2 gene is a major regulatory locus which appears to act in a positive way to turn on the expression of these nitrogen-related enzymes whereas the nit-4 gene appears to mediate nitrate induction of nitrate and nitrite reductase. The nit-3 gene specifies nitrate reductase and is subject to control by both nit-2 and nit-4. Many new nit-2, nit-3, and nit-4 mutants were isolated in order to obtain amber nonsense mutations in these loci which were suppressible by the suppressor gene, Ssu-1. A nit-2 nonsense mutant was isolated which has altered regulatory properties for control of nitrate reductase. L-amino acid oxidase, and uricase, and which may encode a truncated regulatory protein. Four nit-3 nonsense mutations were isolated, each of which completely lacks nitrate reductase activity, which is restored to markedly different levels by suppression with Ssu-1. Studies of heat activation and thermal lability of nitrate reductase suggest a qualitative alteration of the enzyme occurs in two of the Ssu-1 nit-3 strains.
authors.affiliation: Department of Biochemistry, Ohio State University, Columbus 43210.
authors.forename: K G
authors.initials: KG
authors.lastname: Perrine
authors.forename: G A
authors.initials: GA
authors.lastname: Marzluf
mesh_terms: D005796:Genes; D005800:Genes, Fungal; D005809:Genes, Regulator; D009154:Mutation; D009491:Neurospora / Q000235:genetics*; D009492:Neurospora crassa / Q000235:genetics* / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D013489:Suppression, Genetic
chemical_list: D009584:Nitrogen