# LexA repressor

> Mediated Wiki article. Canonical URL: https://mediated.wiki/source/LexA_repressor
> Markdown URL: https://mediated.wiki/source/LexA_repressor.md
> Source: https://en.wikipedia.org/wiki/LexA_repressor
> Source revision: 1237717219
> License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/)

Prokaryotic protein

Protein domain

LexA DNA binding domain lexa s119a mutant Identifiers Symbol LexA_DNA_bind Pfam PF01726 Pfam clan CL0123 InterPro IPR006199 SCOP2 1leb / SCOPe / SUPFAM Available protein structures: PDB IPR006199 PF01726 (ECOD; PDBsum) AlphaFold IPR006199 PF01726

The **LexA repressor** or **LexA** (Locus for X-ray sensitivity A)[1] is a transcriptional [repressor](/source/Repressor) ([EC](/source/Enzyme_Commission_number) [3.4.21.88](https://enzyme.expasy.org/EC/3.4.21.88)) that represses [SOS response](/source/SOS_response) genes coding primarily for error-prone [DNA polymerases](/source/DNA_polymerase), [DNA repair](/source/DNA_repair) [enzymes](/source/Enzyme) and [cell division](/source/Cell_division) inhibitors.[2] LexA forms *de facto* a [two-component regulatory system](/source/Two-component_regulatory_system) with [RecA](/source/RecA), which senses DNA damage at stalled replication forks, forming monofilaments and acquiring an active conformation capable of binding to LexA and causing LexA to cleave itself, in a process called [autoproteolysis](/source/Proteolysis).[1]

LexA polypeptides contains a two domains: a [DNA-binding domain](/source/DNA-binding_domain) and a [dimerization](/source/Protein_dimer) domain.[3] The dimerization domain binds to other LexA polypeptides to form dumbbell shaped dimers. The DNA-binding domain is a variant form of the [helix-turn-helix](/source/Helix-turn-helix) DNA binding [motif](/source/Protein_motif),[4] and is usually located at the [N-terminus](/source/N-terminus) of the protein.[1] This domain is bound to an [SOS box](/source/SOS_box) upstream of SOS response genes until DNA damage stimulates autoproteolysis.[3]

## Clinical significance

DNA damage can be inflicted by the action of [antibiotics](/source/Antibiotic), [bacteriophages](/source/Bacteriophage), and [UV light](/source/UV_light).[2] Of potential clinical interest is the induction of the SOS response by antibiotics, such as [ciprofloxacin](/source/Ciprofloxacin). Bacteria require [topoisomerases](/source/Topoisomerase) such as [DNA gyrase](/source/DNA_gyrase) or [topoisomerase IV](/source/Topoisomerase_IV) for [DNA replication](/source/DNA_replication). Antibiotics such as ciprofloxacin are able to prevent the action of these molecules by attaching themselves to the gyrate–DNA complex, leading to replication fork stall and the induction of the SOS response. The expression of error-prone polymerases under the SOS response increases the basal mutation rate of bacteria. While mutations are often lethal to the cell, they can also enhance survival. In the specific case of topoisomerases, some bacteria have mutated one of their amino acids so that the ciprofloxacin can only create a weak bond to the topoisomerase. This is one of the methods that bacteria use to become [resistant](/source/Antibiotic_resistance) to antibiotics. Ciprofloxacin treatment can therefore potentially lead to the generation of mutations that may render bacteria resistant to ciprofloxacin. In addition, ciprofloxacin has also been shown to induce via the SOS response dissemination of [virulence factors](/source/Virulence_factor)[5] and [antibiotic resistance](/source/Antibiotic_resistance) determinants,[6] as well as the activation of [integron](/source/Integron) [integrases](/source/Integrase),[7] potentially increasing the likelihood of acquisition and dissemination of antibiotic resistance by bacteria.[2]

Impaired LexA proteolysis has been shown to interfere with ciprofloxacin resistance.[8] This offers potential for [combination therapy](/source/Combination_therapy) that combines [quinolones](/source/Quinolone_antibiotic) with strategies aimed at interfering with the action of LexA, either directly or via RecA.

## References

1. ^ [***a***](#cite_ref-Butala2009_1-0) [***b***](#cite_ref-Butala2009_1-1) [***c***](#cite_ref-Butala2009_1-2) Butala M, Žgur-Bertok D, Busby SJ (January 2009). ["The bacterial LexA transcriptional repressor"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11131485). *Cellular and Molecular Life Sciences*. **66** (1): 82–93. [doi](/source/Doi_(identifier)):[10.1007/s00018-008-8378-6](https://doi.org/10.1007%2Fs00018-008-8378-6). [PMC](/source/PMC_(identifier)) [11131485](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11131485). [PMID](/source/PMID_(identifier)) [18726173](https://pubmed.ncbi.nlm.nih.gov/18726173). [S2CID](/source/S2CID_(identifier)) [29537019](https://api.semanticscholar.org/CorpusID:29537019).

1. ^ [***a***](#cite_ref-Er07_2-0) [***b***](#cite_ref-Er07_2-1) [***c***](#cite_ref-Er07_2-2) Erill I, Campoy S, Barbé J (November 2007). ["Aeons of distress: an evolutionary perspective on the bacterial SOS response"](https://ddd.uab.cat/record/288365). *FEMS Microbiology Reviews*. **31** (6): 637–656. [doi](/source/Doi_(identifier)):[10.1111/j.1574-6976.2007.00082.x](https://doi.org/10.1111%2Fj.1574-6976.2007.00082.x). [PMID](/source/PMID_(identifier)) [17883408](https://pubmed.ncbi.nlm.nih.gov/17883408).

1. ^ [***a***](#cite_ref-SnyderChamp_3-0) [***b***](#cite_ref-SnyderChamp_3-1) Henkin TM, Peters JE (2020). "DNA Repair and Mutagenesis". *Snyder and Champness molecular genetics of bacteria* (Fifth ed.). Hoboken, NJ : Washington, D.C: John Wiley & Sons, Inc. [ISBN](/source/ISBN_(identifier)) [9781555819750](https://en.wikipedia.org/wiki/Special:BookSources/9781555819750).

1. **[^](#cite_ref-pmid8076591_4-0)** Fogh RH, Ottleben G, Rüterjans H, Schnarr M, Boelens R, Kaptein R (September 1994). ["Solution structure of the LexA repressor DNA binding domain determined by 1H NMR spectroscopy"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC395313). *The EMBO Journal*. **13** (17): 3936–3944. [doi](/source/Doi_(identifier)):[10.1002/j.1460-2075.1994.tb06709.x](https://doi.org/10.1002%2Fj.1460-2075.1994.tb06709.x). [PMC](/source/PMC_(identifier)) [395313](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC395313). [PMID](/source/PMID_(identifier)) [8076591](https://pubmed.ncbi.nlm.nih.gov/8076591).

1. **[^](#cite_ref-5)** Ubeda C, Maiques E, Knecht E, Lasa I, Novick RP, Penadés JR (May 2005). ["Antibiotic-induced SOS response promotes horizontal dissemination of pathogenicity island-encoded virulence factors in staphylococci"](https://doi.org/10.1111%2Fj.1365-2958.2005.04584.x). *Molecular Microbiology*. **56** (3): 836–844. [doi](/source/Doi_(identifier)):[10.1111/j.1365-2958.2005.04584.x](https://doi.org/10.1111%2Fj.1365-2958.2005.04584.x). [PMID](/source/PMID_(identifier)) [15819636](https://pubmed.ncbi.nlm.nih.gov/15819636).

1. **[^](#cite_ref-6)** Beaber JW, Hochhut B, Waldor MK (January 2004). "SOS response promotes horizontal dissemination of antibiotic resistance genes". *Nature*. **427** (6969): 72–74. [Bibcode](/source/Bibcode_(identifier)):[2004Natur.427...72B](https://ui.adsabs.harvard.edu/abs/2004Natur.427...72B). [doi](/source/Doi_(identifier)):[10.1038/nature02241](https://doi.org/10.1038%2Fnature02241). [PMID](/source/PMID_(identifier)) [14688795](https://pubmed.ncbi.nlm.nih.gov/14688795). [S2CID](/source/S2CID_(identifier)) [4300746](https://api.semanticscholar.org/CorpusID:4300746).

1. **[^](#cite_ref-7)** Guerin E, Cambray G, Sanchez-Alberola N, Campoy S, Erill I, Da Re S, et al. (May 2009). ["The SOS response controls integron recombination"](https://ddd.uab.cat/record/288366). *Science*. **324** (5930): 1034. [Bibcode](/source/Bibcode_(identifier)):[2009Sci...324.1034G](https://ui.adsabs.harvard.edu/abs/2009Sci...324.1034G). [doi](/source/Doi_(identifier)):[10.1126/science.1172914](https://doi.org/10.1126%2Fscience.1172914). [PMID](/source/PMID_(identifier)) [19460999](https://pubmed.ncbi.nlm.nih.gov/19460999). [S2CID](/source/S2CID_(identifier)) [42334786](https://api.semanticscholar.org/CorpusID:42334786).

1. **[^](#cite_ref-8)** Cirz RT, Chin JK, Andes DR, de Crécy-Lagard V, Craig WA, Romesberg FE (June 2005). ["Inhibition of mutation and combating the evolution of antibiotic resistance"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1088971). *PLOS Biology*. **3** (6): e176. [doi](/source/Doi_(identifier)):[10.1371/journal.pbio.0030176](https://doi.org/10.1371%2Fjournal.pbio.0030176). [PMC](/source/PMC_(identifier)) [1088971](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1088971). [PMID](/source/PMID_(identifier)) [15869329](https://pubmed.ncbi.nlm.nih.gov/15869329).

This article incorporates text from the public domain [Pfam](/source/Pfam) and [InterPro](/source/InterPro): [IPR006199](https://www.ebi.ac.uk/interpro/entry/IPR006199)

v t e Endopeptidases: serine proteases/serine endopeptidases (EC 3.4.21) Digestive enzymes Enteropeptidase Trypsin Chymotrypsin Elastase Neutrophil Pancreatic Coagulation factors: Thrombin Factor VIIa Factor IXa Factor Xa Factor XIa Factor XIIa Kallikrein PSA KLK1 KLK2 KLK3 KLK4 KLK5 KLK6 KLK7 KLK8 KLK9 KLK10 KLK11 KLK12 KLK13 KLK14 KLK15 fibrinolysis: Plasmin Plasminogen activator Tissue-type plasminogen activator Urinary plasminogen activator Complement system Factor B Factor D Factor I MASP MASP1 MASP2 C3-convertase Other immune system Chymase Granzyme Tryptase Proteinase 3/Myeloblastin Venombin Ancrod Batroxobin Other Acrosin Prolyl endopeptidase Pronase Proprotein convertases 1 2 Prostasin Reelin Subtilisin/Furin/S1P4 Sedolisin/TPP1 Streptokinase Cathepsin A G

v t e Enzymes Activity Active site Binding site Catalytic triad Oxyanion hole Enzyme promiscuity Diffusion-limited enzyme Cofactor Enzyme catalysis Regulation Allosteric regulation Cooperativity Enzyme inhibitor Enzyme activator Classification EC number Enzyme superfamily Enzyme family List of enzymes Kinetics Enzyme kinetics Eadie–Hofstee diagram Hanes–Woolf plot Lineweaver–Burk plot Michaelis–Menten kinetics Types EC1 Oxidoreductases (list) EC2 Transferases (list) EC3 Hydrolases (list) EC4 Lyases (list) EC5 Isomerases (list) EC6 Ligases (list) EC7 Translocases (list)

v t e DNA repair Excision repair Base excision repair/AP site DNA glycosylase Uracil-DNA glycosylase Poly ADP ribose polymerase Nucleotide excision repair/ERCC XPA XPB XPC XPD/ERCC2 XPE/DDB1 XPF/DDB1 XPG/ERCC5 ERCC1 RPA RAD23A RAD23B Excinuclease DNA mismatch repair MLH1 MSH2 Homologous recombination RecA RecBCD RecF pathway RecQ helicase RAD51 Sgs1 Slx4 LexA Other pathways Transcription-coupled repair ERCC6 ERCC8 Homology directed repair Non-homologous end joining Ku Microhomology-mediated end joining Postreplication repair Photolyase CRY1 CRY2 Regulation SOS box SOS response Other/ungrouped Ogt PcrA Proliferating Cell Nuclear Antigen 8-Oxoguanine Adaptive response Meiotic recombination checkpoint DNA helicase: BLM WRN FANC proteins: core protein complex FANCA FANCB FANCC FANCE FANCF FANCG FANCL FANCM FANCD1 FANCD2 FANCI FANCJ FANCN Category

[Portal](https://en.wikipedia.org/wiki/Wikipedia:Contents/Portals):
- [Biology](https://en.wikipedia.org/wiki/Portal:Biology)

---
Adapted from the Wikipedia article [LexA repressor](https://en.wikipedia.org/wiki/LexA_repressor) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/LexA_repressor?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.