Disease relevance of ilvB

• The ilvB locus of Escherichia coli K-12 is an operon encoding both subunits of acetohydroxyacid synthase I [1].
• Regulation of expression of the ilvB operon in Salmonella typhimurium [2].
• The valine toxicity of these ilvG mutants of S. typhimurium was overcome by increasing the level of acetohydroxy acid synthase I. Enzyme activity could be elevated either by maximally derepressing expression with severe leucine limitation, by introduction of either ilvB or crp on a multicopy plasmid, or by the presence of the ilv-513 mutation [2].
• This activity is encoded by an ilvB gene belonging to a putative operon which contains genes highly similar to the genes of the branched chain amino acid (BCAA) operon of Lactococcus lactis subsp. lactis [3].

High impact information on ilvB

• On the basis of possible secondary structures of ilvB leader RNA, we predicted that attenuation of this operon should also be affected by growth of cells in limiting amounts of alanine or threonine [4].
• The DNA sequence of the promoter-regulatory region of the ilvB operon of Escherichia coli was determined [5].
• In vitro transcription from the ilvB promoter was greatly increased by cyclic AMP and CRP [5].
• The deduced amino acid sequence shares homology with the large subunits of the acetohydroxy acid synthase isozymes I, II, and III, encoded by the ilvB, ilvG, and ilvI genes of E. coli [6].
• We reserve the designation ilvB for the promoter proximal (longer) cistron and designate the promoter distal cistron ilvN [1].

Chemical compound and disease context of ilvB

• The ilvB gene of Salmonella typhimurium encodes the valine-sensitive form of acetohydroxy acid synthase, acetohydroxy acid synthase I, which catalyzes the first step in the parallel biosynthesis of isoleucine and valine [2].
• Starvation for ilvB operon leader amino acids other than leucine or valine does not increase acetohydroxy acid synthase activity in Escherichia coli [7].
• Instability of ilvB expression in E. coli was the consequence of a frequent IS5 insertion sequence in this gene [3].

Biological context of ilvB

• On the basis of these data, a model for multivalent attenuation of the ilvB operon is presented [8].
• The ilvB gene of Escherichia coli K12 has been cloned into a multicopy plasmid [8].
• The nucleotide sequence of a regulatory region preceding the ilvB structural gene has been determined [8].
• The molecular weight and amino acid sequence of the ilvB polypeptide are strikingly similar to those of the I1vI (larger subunit of AHAS III) and I1vG (larger subunit of AHAS II) polypeptides [1].
• The ilvB locus of Escherichia coli K-12 encloses two open reading frames defining polypeptides of 60,000 and 11,200 molecular weight [1].

Associations of ilvB with chemical compounds

• Nucleotide sequence of the ilvB promoter-regulatory region: a biosynthetic operon controlled by attenuation and cyclic AMP [5].
• 5. Expression of ilvB was shown to be nearly completely repressed by the end products leucine and valine [2].
• This mutation, which is closely linked to genes encoding the phosphoenol pyruvate:sugar phosphotransferase system (pts), causes highly elevated expression of ilvB that is refractory to repression by leucine and valine, as is the major ilv operon [2].
• C. crescentus strains resistant to the herbicide sulfometuron methyl, which is known to inhibit the action of certain acetohydroxyacid synthases in a variety of bacteria and plants, were shown to contain mutations at the ilvB locus, further suggesting that an acetohydroxyacid synthase gene resides at this locus [9].

Analytical, diagnostic and therapeutic context of ilvB

• The orientation of the ilvB operon relative to plasmid genes was determined by restriction enzyme mapping [10].

References