Disease relevance of narB

• The recombinant NR encoded by the narB gene of Synechococcus sp. strain RF-1, expressed in E. coli, also showed the biphasic kinetics with similar pH and temperature profiles [1].
• The NtcA-like promoters found upstream of nirA, nrtP, and narB all differ in sequence from the canonical NtcA promoter established for other cyanobacteria, and in the case of nirA, the NtcA-like promoter was functional only in cells deprived of combined nitrogen [2].
• Unlike the situation in A. nidulans, nitrate appeared to play an active role in nitrate reductase synthesis in the filamentous nitrogen-fixing strains Anabaena sp. strain 7119 and Nostoc sp. strain 6719, with ammonium acting as an antagonist with regard to nitrate [3].
• DNA probes from the narG gene of Escherichia coli, which encodes the large polypeptide of respiratory nitrate reductase, show cross-hybridization at low stringency to a single region of the genome of the cyanobacterium Synechococcus PCC6301 [4].

High impact information on narB

• In the presence of ammonium, NC2 could not assimilate nitrate despite its ability to accumulate nitrate intracellularly, which suggested that reduction of intracellular nitrate by nitrate reductase is also subject to inhibition by ammonium [5].
• A Phi(nasA-lacZ) fusion has been used to analyse expression of the nasAB operon in three different genetic backgrounds with altered nitrate reductase activity [6].
• Nitrate reductase contains both molybdenum cofactor and an iron-sulfur cluster [7].
• This finding suggested that the permanent inhibition of nitrate assimilation by an S49A derivative of PII, as was previously reported for Synechococcus elongatus strain PCC 7942, is likely to have resulted from inhibition of nitrate reductase rather than the nitrate and nitrite transporter [8].
• The genes encoding nitrate reductase (narB) and nitrite reductase (nirA) are clustered on the chromosome but are organized in separate transcriptional units [2].

Chemical compound and disease context of narB

• Integration of a cyanobacterial protein involved in nitrate reduction (narB) into isolated Synechococcus but not into pea thylakoid membranes [9].
• Addition of isopropyl-beta-D-thiogalactoside to E. coli (pCSLM1) resulted in the parallel expression of a 76 kDa polypeptide and a nitrate reductase activity with properties identical to those known for nitrate reductase isolated from Synechococcus cells [10].
• Carbon supply and 2-oxoglutarate effects on expression of nitrate reductase and nitrogen-regulated genes in Synechococcus sp. strain PCC 7942 [11].
• The nar beta gene encodes a protein of 737 amino acid residues, which shows 61% identity to nitrate reductase of the unicellular cyanobacterium Synechococcus sp. PCC 7942 and only weak homologies to different bacterial molybdoenzymes, such as nitrate reductases or formate dehydrogenases [12].

Biological context of narB

• The narB gene from the cyanobacterium Synechococcus sp. PCC 7942 was cloned downstream from the LacI-regulated promoter Ptrc in the Escherichia coli vector pTrc99A, rendering plasmid pCSLM1 [10].
• Cloning of a third nitrate reductase gene from the cyanobacterium Anacystis nidulans R2 using a shuttle cosmid library [13].
• Phosphorylation of PII is thus unlikely to play a role in the regulation of nitrate reductase [14].
• Mutations generated by insertion of an antibiotic-resistance gene cassette into the gene encoding nitrite reductase are associated with reduced expression of nitrate reductase; cotranscription of nitrate assimilation genes in the cluster is inferred from this finding [15].
• Nucleotide sequence of the nar beta gene encoding assimilatory nitrate reductase from the cyanobacterium Oscillatoria chalybea [12].

Anatomical context of narB

• The association of the narB-coded protein with thylakoids might require another membrane protein whose identity is not known [9].
• In thylakoido integration of synthetic proteins resulted in the association of the full-length narB-coded protein to the Synechococcus photosynthetic membranes [9].

Associations of narB with chemical compounds

• There was no significant difference in nitrate reductase activity levels between the two strains, and the nitrite reductase levels were somewhat lower in the mutant than in the wild-type strain [16].
• Transcripts of the nrtP and narB genes were detected in cells grown on nitrate but were not detected in cells grown on urea or ammonia [17].
• Cells of NC2 and its derivative (nitrate reductase-less strain NC4) carrying the truncated NrtC but not the cells with the wild-type NrtC accumulated nitrate intracellularly in the presence of ammonium in medium [5].
• In contrast, a prominent nitrate reductase (NR) activity was detected in diazotrophically grown cells using the reduced methyl viologen assay [1].
• When modified at the N terminus by a polyhistidine tag, the recombinant NR activity was shifted from biphasic to hyperbolic kinetics and showed only a single K(m) for nitrate, indicating the functional importance of the NarB N-terminal structure in NR kinetics [1].

References