Disease relevance of gltB

• A mutant (gltB) of Escherichia coli lacking glutamate synthase (GOGAT) was unable to utilize a wide variety of compounds as sole nitrogen source (e.g., arginine, proline, gamma-aminobutyrate, and glycine) [1].
• During the course of this work, the Azospirillum DNA regions flanking the gltD and gltB genes, the genes encoding the GltS beta and alpha subunits, respectively, were sequenced and analyzed [2].
• Nitrogen source regulation of glutamate synthase activity in Bacillus subtilis occurs at the level of transcription of the gltA and gltB genes, which encode the two subunits of the enzyme [3].
• Stress-response sigma factor sigma(H) directs expression of the gltB gene encoding glutamate synthase in Streptomyces coelicolor A3(2) [4].

High impact information on gltB

• The organization of the gltBD region of A. brasilense differs from that of the corresponding region in E. coli: in A. brasilense, gltD is upstream relative to gltB, and its stop codon is separated by 141 bp from the first ATG of gltB [5].
• First, insertions in gltB, gltD or gltF all prevent Ntr induction [6].
• Thus, we conclude that gltB or gltD mutants grow slowly on many poor nitrogen sources because they are starved for glutamate [7].
• The argument that accumulated glutamine represses the Ntr system in gltB or gltD mutants is also incorrect, because these mutants can derepress the Ntr system normally so long as sufficient glutamate is supplied [7].
• A cosmid containing the gltBD region was isolated from a T. ferrooxidans cosmid gene bank, but was unable to complement an E. coli gltB mutant [8].

Biological context of gltB

• Subcloning and nucleotide sequencing of approximately 1,206 bp of DNA encompassing the gltBDF regulatory region showed that the mutations affected the first base at each of the two identical Shine-Dalgarno sequences, SD1 and SD2, located 40 and 8 bases, respectively, upstream from the putative gltB open reading frame [9].
• The results suggest that SD2 is the preferred functional site at which ribosomes initiate gltB mRNA translation [9].
• The other model postulated that mutations in gltB or gltD (which encode the subunits of GOGAT) were polar on a downstream gene, gltF, which is necessary for proper activation of gene expression by the Ntr system [7].
• Two open reading frames of 4548 and 1446 base pairs (bp) were identified within the fragment as the structural genes for the alpha and beta subunits (gltB and gltD, respectively) of A. brasilense GltS [5].
• Plasmid subclones of recombinant phage lambda Asm152 were able to complement both Escherichia coli gltB and A. sesbaniae Asm- Vi mutants; NADPH-glutamate synthase activity was detected in all such strains complemented to Asm+ [10].

Associations of gltB with chemical compounds

• During the course of this study we found that the reported position of the locus (gltB) for glutamate synthase is incorrect [1].
• Because the remaining five A. sesbaniae Asm- mutants mapped to a 1.5-kbp region adjacent to gltA+, these mutants probably define a single gltB+ gene (glutamate dehydrogenase NADPH-dependent L-glutamate synthase subunit); this region did not exhibit homology with the B. subtilis gltB+ gene [10].
• Both the inhibition of growth and the massive accumulation of phosphatidic acid which occur in a cds-8 mutant at pH 8 were suppressed by mutations at a second locus, designated cdsS, which mapped between argG and gltB near min 68 [11].

Other interactions of gltB

• gltB gene and regulation of nitrogen metabolism by glutamine synthetase in Escherichia coli [1].

References