Editing Tryptophan repressor (section)

{{short description|Transcription factor}}
{{Infobox protein family
| Symbol = Trp_repressor
| Name = Trp repressor protein
| image = TrpR.jpg
| width = 
| caption = [[Ribbon diagram]] of the trpR protein
| Pfam = PF01371
| Pfam_clan = CL0123
| InterPro = IPR000831
| SMART = 
| PROSITE = 
| MEROPS =
| SCOP = 2wrp
| TCDB = 
| OPM family = 
| OPM protein = 
| CAZy = 
| CDD =
}}
{{Infobox nonhuman protein
| Name = Trp operon repressor
| image = 
| width = 
| caption = 
| Organism = ''Escherichia coli''
| TaxID = 511145
| Symbol = trpR
| AltSymbols = 
| EntrezGene = 948917
| PDB = 
| RefSeqmRNA =
| RefSeqProtein = NP_418810
| UniProt = P0A881
| ECnumber = 
| Chromosome = genome
| EntrezChromosome = NC_000913
| GenLoc_start = 4630733
| GenLoc_end = 4631157
}}

'''Tryptophan repressor''' (or '''trp repressor''') is a [[transcription factor]] involved in controlling [[amino acid]] metabolism. It has been best studied in ''[[Escherichia coli]]'', where it is a dimeric protein that regulates transcription of the 5 genes in the tryptophan [[operon]].<ref>{{cite journal |vauthors=Santillan M, Mackey MC |title=Dynamic regulation of the tryptophan operon: A modeling study and comparison with experimental data |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=98 |issue=4 |pages=1364–9 |year=2001 |pmid=11171956 |doi=10.1073/pnas.98.4.1364 |pmc=29262|bibcode=2001PNAS...98.1364S |doi-access=free }}</ref> When the amino acid [[tryptophan]] is plentiful in the cell, it binds to the protein, which causes a conformational change in the protein.<ref>{{cite journal |author=Zhang RG, Joachimiak A, Lawson CL, Schevitz RW, Otwinowski Z, [[Paul Sigler|Sigler PB]] |title=The crystal structure of trp aporepressor at 1.8 A shows how binding tryptophan enhances DNA affinity |journal=Nature |volume=327 |issue=6123 |pages=591–7 |year=1987 |pmid=3600756 |doi=10.1038/327591a0|bibcode=1987Natur.327..591Z |s2cid=4335349 }}</ref> The repressor complex then binds to its operator sequence in the genes it regulates, shutting off the genes.<ref>{{cite journal |vauthors=Jeeves M, Evans PD, Parslow RA, Jaseja M, Hyde EI |title=Studies of the Escherichia coli Trp repressor binding to its five operators and to variant operator sequences |journal=Eur. J. Biochem. |volume=265 |issue=3 |pages=919–28 |year=1999 |pmid=10518785 |doi=10.1046/j.1432-1327.1999.00792.x|doi-access=free }}</ref><ref>{{cite journal |vauthors=Arvidson DN, Arvidson CG, Lawson CL, Miner J, Adams C, Youderian P |title=The tryptophan repressor sequence is highly conserved among the Enterobacteriaceae |journal=Nucleic Acids Res. |volume=22 |issue=10 |pages=1821–9 |year=1994 |pmid=8208606 |doi=10.1093/nar/22.10.1821 |pmc=308080}}</ref>

One of the genes regulated by trp repressor, [[trpR]], codes for the tryptophan repressor protein itself.  This is a form of [[negative feedback|feedback regulation]]. However, these genes are located on different operons.

The (tryptophan) repressor is a 25 kD [[protein]] homodimer which regulates [[transcription (genetics)|transcription]] of the [[tryptophan]] biosynthetic pathway in [[bacteria]].  There are 5 operons which are regulated by trpR: the ''trpEDCBA'', ''trpR'', ''AroH'', ''AroL'', and ''mtr'' operons.