Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.7.1.4 (nitrite reductase)
 1,847 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

nit-4 is a pathway-specific regulatory gene which controls nitrate assimilation in Neurospora crassa, and appears to mediate nitrate induction of nitrate and nitrite reductase. The NIT4 protein consists of 1090 amino-acid residues and possesses a single GAL4-like putative DNA-binding domain plus acidic, glutamine-rich, and polyglutamine regions. Several mutants with amino-acid substitutions in the putative DNA-binding domain and a nit-4 deletion mutant, which encodes a truncated NIT4 protein lacking the polyglutamine region, are functional, i.e., they are capable of transforming a nit-4 mutant strain. However, transformants obtained with most of these nit-4 mutant genes possess a markedly reduced level of nitrate reductase and grow only slowly on nitrate, emphasizing the need to examine quantitatively the affects of in vitro-manipulated genes. The possibility that some mutant genes could yield transformants only if multiple copies were integrated was examined. The presence of multiple copies of wild-type or mutant nit-4 genes did not generally lead to increased enzyme activity or growth rate, but instead frequently appeared to be detrimental to nit-4 function. A hybrid nit-4-nirA gene transforms nit-4 mutants but only allows slow growth on nitrate and has a very low level of nitrate reductase.
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PMID:Transformants of Neurospora crassa with the nit-4 nitrogen regulatory gene: copy number, growth rate and enzyme activity. 138 9

The nucleotide sequence of nirA, mediating nitrate induction in Aspergillus nidulans, has been determined. Alignment of the cDNA and the genomic DNA sequence indicates that the gene contains four introns and encodes a protein of 892 amino acids. The deduced NIRA protein displays all characteristics of a transcriptional activator. A putative double-stranded DNA-binding domain in the amino-terminal part comprises six cysteine residues, characteristic for the GAL4 family of zinc finger proteins. An amino-terminal highly acidic region and two proline-rich regions are also present. The nucleotide sequences of two mutations were determined after they were mapped by transformation with overlapping DNA fragments, amplified by the polymerase chain reaction. nirA87, a mutation conferring noninducibility by nitrate and nitrite, has a -1 frameshift at triplet 340, which eliminates 549 C-terminal amino acids from the polypeptide. Under the assumption that the truncated polypeptide is stable, it comprises the zinc finger domain and the acidic region, which seem not sufficient for transcriptional activation. nirAd-106, an allele conferring nitrogen metabolite derepression of nitrate and nitrite reductase activity, includes two transitions, changing a glutamic acid to a lysine and a valine to an alanine, situated between a basic and a proline-rich region of the protein. Northern (RNA) analysis of the wild type and of constitutive (nirAc) and derepressed (nirAd) mutants show that the nirA transcript does not vary between these strains, being in all cases constitutively expressed. On the other hand, transcript levels of structural genes (niaD and niiA) do vary, being highly inducible in the wild type but constitutively expressed in the nirAc mutant. The nirAd mutant appears phenotypically derepressed, because the niaD and niiA transcript levels are overinduced in the presence of nitrate but are still partially repressed in the presence of ammonium.
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PMID:nirA, the pathway-specific regulatory gene of nitrate assimilation in Aspergillus nidulans, encodes a putative GAL4-type zinc finger protein and contains four introns in highly conserved regions. 192 75

The expression of the structural genes nit-3 and nit-6, which encode the nitrate assimilatory enzymes nitrate reductase and nitrite reductase, respectively, is highly regulated by the global-acting NIT2 regulatory protein. These structural genes are also controlled by nitrogen catabolite repression and by specific induction via nitrate. A pathway-specific regulatory protein, NIT4, appears to mediate nitrate induction of nit-3 and of nit-6. The NIT4 protein, composed of 1090 amino acids, contains a putative GAL4-like Cys-6 zinc cluster DNA-binding motif, which is joined by a short segment to a stretch of amino acids that appear to constitute a coiled-coil dimerization domain. Chemical crosslinking studies demonstrated that a truncated form of NIT4 forms homodimers. Mobility-shift and DNA-footprinting experiments have identified two NIT4-binding sites of significantly different strengths in the promoter region of the nit-3 gene. The stronger binding site contains a symmetrical octameric sequence, TCCGCGGA, whereas the weaker site has a related sequence. Sequences related to this palindromic element can be found upstream of the nit-6 gene.
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PMID:Sequence-specific DNA binding by NIT4, the pathway-specific regulatory protein that mediates nitrate induction in Neurospora. 759 94

Expression of nit-3 and nit-6, the structural genes which encode nitrate reductase and nitrite reductase in Neurospora crassa, requires the global-acting NIT2 and the pathway specific NIT4 regulatory proteins. NIT4, which consists of 1090 amino-acid residues, possesses a Cys6/Zn2 zinc cluster DNA-binding-domain. NIT4 was dissected to localize transactivation domains by fusion of various segments of NIT4 to the DNA-binding domain of GAL4 for in vivo analysis in yeast. Three separate activation subdomains, and one negative-acting region, which function in yeast were located in the carboxyl-terminal region of NIT4. The C-terminal tail of 28 amino-acid residues was identified as a minimal activation domain and consists of a novel leucine-rich, acidic region. Most deletions which removed even small segments of the NIT4 protein were found to lead to the loss of NIT4 function in vivo in N. crassa, implying that the central region of the protein which lies between the DNA-binding and activation domains is essential for function. The yeast two-hybrid system was employed to identify regions of NIT4 responsible for dimer formation. A short isoleucine-rich segment downstream from the zinc cluster, predicted to form a coiled coil, allowed dimerization in vivo; this same isoleucine-rich region also showed dimerization in vitro when examined via chemical cross linking. The enzyme nitrate reductase has been postulated to exert autogenous regulation by directly interacting with the NIT4 protein. This possible nitrate reductase-NIT4 interaction was investigated with the yeast two-hybrid system and by direct in vitro binding assays; both assays failed to identify such a protein-protein interaction.
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PMID:The regulatory protein NIT4 that mediates nitrate induction in Neurospora crassa contains a complex tripartite activation domain with a novel leucine-rich, acidic motif. 866 93