title: Cooperative action of the NIT2 and NIT4 transcription factors upon gene expression in Neurospora crassa.
abstract: In Neurospora crassa, the nit-3 gene, which encodes nitrate reductase, an enzyme required for the utilization of inorganic nitrate, is subject to a high degree of genetic and metabolic regulation as a member of the nitrogen control circuit. The nit-3 gene promoter contains binding sites for a globally acting protein NIT2 and a pathway-specific protein NIT4. Expression of the nit-3 gene absolutely requires both the NIT2 and NIT4 transcription factors and only occurs under conditions of nitrogen source derepression and nitrate induction. In the sulfur control circuit, the cys-14 gene encodes sulfate permease II, which facilitates the assimilation of sulfate. Expression of cys-14 is strongly regulated by only a single positive-acting factor, CYS3. It was of interest to determine whether NIT2 or NIT4 alone was capable of turning on the expression of cys-14, since this structural gene is normally controlled by only one regulatory protein. NIT2- and/or NIT4-binding elements were introduced into the promoter of a wild-type cys-14 gene and these constructs were transformed into a cys-13(-) cys-14(-) mutant strain and into a nit-2(-) mutant host. We examined whether any of these cys-14 genes in these transformants could now be controlled as a nitrogen-regulated gene. Sulfate permease assays revealed that both NIT2 and NIT4 were required for cys-14 expression upon nitrate induction, while neither alone activated any detectable cys-14 expression. We thus conclude that neither NIT2 nor NIT4 is capable alone of activating gene expression in this context, but together they can cooperate to elicit strong activation.
authors.affiliation: Department of Biochemistry, Ohio State Biochemistry Program, Ohio State University, 484 West 12th Avenue, Columbus, OH 43210, USA.
authors.forename: Xiaokui
authors.initials: X
authors.lastname: Mo
authors.forename: George A
authors.initials: GA
authors.lastname: Marzluf
mesh_terms: D000595:Amino Acid Sequence; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D008969:Molecular Sequence Data; D009492:Neurospora crassa / Q000235:genetics*; D010957:Plasmids; D011994:Recombinant Proteins / Q000378:metabolism; D015183:Restriction Mapping; D015534:Trans-Activators; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D027321:Anion Transport Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C068100:NIT2 protein, Neurospora crassa; D011994:Recombinant Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C071240:NIT-4 protein, Neurospora crassa; C022702:sulfate permease