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Proc Natl Acad Sci U S A. Jul 1981; 78(7): 4199–4203.
PMCID: PMC319756

Purified lexA protein is a repressor of the recA and lexA genes.


Escherichia coli shows a pleiotropic response (the SOS response) to treatments that damage DNA or inhibit DNA replication. Previous evidence has suggested that the product of the lexA gene is involved in regulating the SOS response, perhaps as a repressor, and that it is sensitive to the recA protease. We show here that lexA protein is a repressor of at least two genes, recA and lexA. Purified protein bound specifically to the regulatory regions of the two genes, as judged by DNase I protection experiments, and it specifically inhibited in vitro transcription of both genes. The binding sites in recA and lexA were found to be about 20 base pairs (bp) and 40 bp long, respectively. The 40-bp sequence in lexA was composed of two adjacent 20-bp sequences, which had considerable homology to one another and to the corresponding recA sequence. These 20-bp sequences, which we term "SOS boxes," show considerable inverted repeat structure as well. These features suggest that each box represents a single repressor binding site. Finally, we found that purified lexA protein was a substrate for the recA protease in a reaction requiring ATP or an analogue, adenosine 5'-[gamma-thio]triphosphate, and denatured DNA.

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  • Witkin EM. Ultraviolet mutagenesis and inducible DNA repair in Escherichia coli. Bacteriol Rev. 1976 Dec;40(4):869–907. [PMC free article] [PubMed]
  • Roberts JW, Roberts CW, Craig NL. Escherichia coli recA gene product inactivates phage lambda repressor. Proc Natl Acad Sci U S A. 1978 Oct;75(10):4714–4718. [PMC free article] [PubMed]
  • Craig NL, Roberts JW. E. coli recA protein-directed cleavage of phage lambda repressor requires polynucleotide. Nature. 1980 Jan 3;283(5742):26–30. [PubMed]
  • Gudas LJ, Pardee AB. Model for regulation of Escherichia coli DNA repair functions. Proc Natl Acad Sci U S A. 1975 Jun;72(6):2330–2334. [PMC free article] [PubMed]
  • Gudas LJ, Mount DW. Identification of the recA (tif) gene product of Escherichia coli. Proc Natl Acad Sci U S A. 1977 Dec;74(12):5280–5284. [PMC free article] [PubMed]
  • McEntee K. Protein X is the product of the recA gene of Escherichia coli. Proc Natl Acad Sci U S A. 1977 Dec;74(12):5275–5279. [PMC free article] [PubMed]
  • Emmerson PT, West SC. Identification of protein X of Escherichia coli as the recA+/tif+ gene product. Mol Gen Genet. 1977 Sep 21;155(1):77–85. [PubMed]
  • Little JW, Harper JE. Identification of the lexA gene product of Escherichia coli K-12. Proc Natl Acad Sci U S A. 1979 Dec;76(12):6147–6151. [PMC free article] [PubMed]
  • Brent R, Ptashne M. The lexA gene product represses its own promoter. Proc Natl Acad Sci U S A. 1980 Apr;77(4):1932–1936. [PMC free article] [PubMed]
  • Kenyon CJ, Walker GC. DNA-damaging agents stimulate gene expression at specific loci in Escherichia coli. Proc Natl Acad Sci U S A. 1980 May;77(5):2819–2823. [PMC free article] [PubMed]
  • Little JW, Edmiston SH, Pacelli LZ, Mount DW. Cleavage of the Escherichia coli lexA protein by the recA protease. Proc Natl Acad Sci U S A. 1980 Jun;77(6):3225–3229. [PMC free article] [PubMed]
  • McPartland A, Green L, Echols H. Control of recA gene RNA in E. coli: regulatory and signal genes. Cell. 1980 Jul;20(3):731–737. [PubMed]
  • Pacelli LZ, Edmiston SH, Mount DW. Isolation and characterization of amber mutations in the lexA gene of Escherichia coli K-12. J Bacteriol. 1979 Jan;137(1):568–573. [PMC free article] [PubMed]
  • Mount DW, Low KB, Edmiston SJ. Dominant mutations (lex) in Escherichia coli K-12 which affect radiation sensitivity and frequency of ultraviolet lght-induced mutations. J Bacteriol. 1972 Nov;112(2):886–893. [PMC free article] [PubMed]
  • Kenyon CJ, Walker GC. Expression of the E. coli uvrA gene is inducible. Nature. 1981 Feb 26;289(5800):808–810. [PubMed]
  • Fogliano M, Schendel PF. Evidence for the inducibility of the uvrB operon. Nature. 1981 Jan 15;289(5794):196–198. [PubMed]
  • Brent R, Ptashne M. Mechanism of action of the lexA gene product. Proc Natl Acad Sci U S A. 1981 Jul;78(7):4204–4208. [PMC free article] [PubMed]
  • Sancar A, Hack AM, Rupp WD. Simple method for identification of plasmid-coded proteins. J Bacteriol. 1979 Jan;137(1):692–693. [PMC free article] [PubMed]
  • Little JW. Isolation of recombinant plasmids and phage carrying the lexA gene of Escherichia coli K-12. Gene. 1980 Aug;10(3):237–247. [PubMed]
  • Müller-Hill B. Lac repressor and lac operator. Prog Biophys Mol Biol. 1975;30(2-3):227–252. [PubMed]
  • Johnsrud L. Contacts between Escherichia coli RNA polymerase and a lac operon promoter. Proc Natl Acad Sci U S A. 1978 Nov;75(11):5314–5318. [PMC free article] [PubMed]
  • Bolivar F, Rodriguez RL, Greene PJ, Betlach MC, Heyneker HL, Boyer HW, Crosa JH, Falkow S. Construction and characterization of new cloning vehicles. II. A multipurpose cloning system. Gene. 1977;2(2):95–113. [PubMed]
  • Little JW. Construction and characterization of a plasmid coding for a fragment of the Escherichia coli recA protein. Mol Gen Genet. 1979;177(1):13–22. [PubMed]
  • Horii T, Ogawa T, Ogawa H. Organization of the recA gene of Escherichia coli. Proc Natl Acad Sci U S A. 1980 Jan;77(1):313–317. [PMC free article] [PubMed]
  • Sancar A, Stachelek C, Konigsberg W, Rupp WD. Sequences of the recA gene and protein. Proc Natl Acad Sci U S A. 1980 May;77(5):2611–2615. [PMC free article] [PubMed]
  • Ross W, Landy A, Kikuchi Y, Nash H. Interaction of int protein with specific sites on lambda att DNA. Cell. 1979 Oct;18(2):297–307. [PMC free article] [PubMed]
  • Maxam AM, Gilbert W. Sequencing end-labeled DNA with base-specific chemical cleavages. Methods Enzymol. 1980;65(1):499–560. [PubMed]
  • Meyer BJ, Kleid DG, Ptashne M. Lambda repressor turns off transcription of its own gene. Proc Natl Acad Sci U S A. 1975 Dec;72(12):4785–4789. [PMC free article] [PubMed]
  • Phizicky EM, Roberts JW. Kinetics of RecA protein-directed inactivation of repressors of phage lambda and phage P22. J Mol Biol. 1980 May 25;139(3):319–328. [PubMed]
  • Little JW, Hanawalt PC. Induction of protein X in Escherichia coli. Mol Gen Genet. 1977 Feb 15;150(3):237–248. [PubMed]
  • Bradford MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976 May 7;72:248–254. [PubMed]
  • Galas DJ, Schmitz A. DNAse footprinting: a simple method for the detection of protein-DNA binding specificity. Nucleic Acids Res. 1978 Sep;5(9):3157–3170. [PMC free article] [PubMed]
  • Johnson AD, Meyer BJ, Ptashne M. Interactions between DNA-bound repressors govern regulation by the lambda phage repressor. Proc Natl Acad Sci U S A. 1979 Oct;76(10):5061–5065. [PMC free article] [PubMed]
  • Horii T, Ogawa T, Ogawa H. Nucleotide sequence of the lexA gene of E. coli. Cell. 1981 Mar;23(3):689–697. [PubMed]
  • Miki T, Ebina Y, Kishi F, Nakazawa A. Organization of the lexA gene of Escherichia coli and nucleotide sequence of the regulatory region. Nucleic Acids Res. 1981 Feb 11;9(3):529–543. [PMC free article] [PubMed]
  • Meyer BJ, Maurer R, Ptashne M. Gene regulation at the right operator (OR) of bacteriophage lambda. II. OR1, OR2, and OR3: their roles in mediating the effects of repressor and cro. J Mol Biol. 1980 May 15;139(2):163–194. [PubMed]

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