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Pathway Description
Operon: Acetolactate Synthase III Activation
Escherichia coli
Category:
Protein Pathway
Sub-Categories:
Gene Regulatory
Cellular Response
Created: 2015-09-09
Last Updated: 2019-08-19
The ilvIH operon in E. coli contains two genes that encode the two subunits of the acetolactate synthase isozyme 3 protein. This protein is used in the biosynthesis of L-isoleucine in the bacteria. The operon is activated by the binding of the leucine-responsive regulatory protein (Lrp) to either of two regions upstream of the promoter. Binding of Lrp to the first upstream region (between -260 and -190) appears to be required for operon transcription, while binding to the downstream region (between -150 and -40) enhances it without being required. The operon can also be negatively regulated by the binding of the DNA-binding protein H-NS, which binds to DNA, altering its structure and preventing RNA polymerase from binding and transcribing the operon. The operon is also negatively regulated by the presence of leucine in the cell, which binds to Lrp, changing its conformation and preventing it from binding to its target sites in the operon. This means that if leucine is present in the cell in high enough concentrations, the operon will be inactivated.
The genes in the operon, ilvI and ilvH, encode the acetolactate synthase isozyme 3 large and small subunits respectively. Two large and two small subunits combine to form the final enzyme, which is responsible for the conversion of pyruvate in the cell to (2S)-2-acetolactate, which is then used in future steps to form L-isoleucine.
References
Operon: Acetolactate Synthase III Activation References
Platko JV, Willins DA, Calvo JM: The ilvIH operon of Escherichia coli is positively regulated. J Bacteriol. 1990 Aug;172(8):4563-70.
Pubmed: 2115869
Jafri S, Chen S, Calvo JM: ilvIH operon expression in Escherichia coli requires Lrp binding to two distinct regions of DNA. J Bacteriol. 2002 Oct;184(19):5293-300. doi: 10.1128/jb.184.19.5293-5300.2002.
Pubmed: 12218014
Squires CH, De Felice M, Devereux J, Calvo JM: Molecular structure of ilvIH and its evolutionary relationship to ilvG in Escherichia coli K12. Nucleic Acids Res. 1983 Aug 11;11(15):5299-313. doi: 10.1093/nar/11.15.5299.
Pubmed: 6308579
Yura T, Mori H, Nagai H, Nagata T, Ishihama A, Fujita N, Isono K, Mizobuchi K, Nakata A: Systematic sequencing of the Escherichia coli genome: analysis of the 0-2.4 min region. Nucleic Acids Res. 1992 Jul 11;20(13):3305-8. doi: 10.1093/nar/20.13.3305.
Pubmed: 1630901
Blattner FR, Plunkett G 3rd, Bloch CA, Perna NT, Burland V, Riley M, Collado-Vides J, Glasner JD, Rode CK, Mayhew GF, Gregor J, Davis NW, Kirkpatrick HA, Goeden MA, Rose DJ, Mau B, Shao Y: The complete genome sequence of Escherichia coli K-12. Science. 1997 Sep 5;277(5331):1453-62. doi: 10.1126/science.277.5331.1453.
Pubmed: 9278503
Willins DA, Ryan CW, Platko JV, Calvo JM: Characterization of Lrp, and Escherichia coli regulatory protein that mediates a global response to leucine. J Biol Chem. 1991 Jun 15;266(17):10768-74.
Pubmed: 2040596
Oshima T, Aiba H, Baba T, Fujita K, Hayashi K, Honjo A, Ikemoto K, Inada T, Itoh T, Kajihara M, Kanai K, Kashimoto K, Kimura S, Kitagawa M, Makino K, Masuda S, Miki T, Mizobuchi K, Mori H, Motomura K, Nakamura Y, Nashimoto H, Nishio Y, Saito N, Horiuchi T, et al.: A 718-kb DNA sequence of the Escherichia coli K-12 genome corresponding to the 12.7-28.0 min region on the linkage map. DNA Res. 1996 Jun 30;3(3):137-55. doi: 10.1093/dnares/3.3.137.
Pubmed: 8905232
Pon CL, Calogero RA, Gualerzi CO: Identification, cloning, nucleotide sequence and chromosomal map location of hns, the structural gene for Escherichia coli DNA-binding protein H-NS. Mol Gen Genet. 1988 May;212(2):199-202. doi: 10.1007/bf00334684.
Pubmed: 2841565
La Teana A, Falconi M, Scarlato V, Lammi M, Pon CL: Characterization of the structural genes for the DNA-binding protein H-NS in Enterobacteriaceae. FEBS Lett. 1989 Feb 13;244(1):34-8. doi: 10.1016/0014-5793(89)81156-1.
Pubmed: 2494066
Falconi M, Gualtieri MT, La Teana A, Losso MA, Pon CL: Proteins from the prokaryotic nucleoid: primary and quaternary structure of the 15-kD Escherichia coli DNA binding protein H-NS. Mol Microbiol. 1988 May;2(3):323-9. doi: 10.1111/j.1365-2958.1988.tb00035.x.
Pubmed: 3135462
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