title: Xer recombination in Escherichia coli. Site-specific DNA topoisomerase activity of the XerC and XerD recombinases.
abstract: Xer site-specific recombination functions in maintaining circular replicons in the monomeric state in Escherichia coli. Two recombinases of the bacteriophage lambda integrase family, XerC and XerD, are required for recombination at the chromosomal site, dif, and at a range of plasmid-borne sites. Xer recombination core sites contain the 11-base pair binding sites for each recombinase separated by a 6 to 8-base pair central region. We report that both XerC and XerD act as site-specific type I topoisomerases by relaxing supercoiled plasmids containing a dif site. Relaxation by either XerC or XerD occurs in the absence of the partner recombinase and requires only a single recombination core site. XerC or XerD relaxation activities are completely inhibited by the addition of the partner recombinase, providing that the DNA recognition sequence for the inhibiting partner is present.
authors.affiliation: Microbiology Unit, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom.
authors.forename: F
authors.initials: F
authors.lastname: Cornet
authors.forename: B
authors.initials: B
authors.lastname: Hallet
authors.forename: D J
authors.initials: DJ
authors.lastname: Sherratt
mesh_terms: D001665:Binding Sites; D004254:DNA Nucleotidyltransferases / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry; D004278:DNA, Superhelical / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D019426:Integrases; D009690:Nucleic Acid Conformation; D010957:Plasmids / Q000378:metabolism; D045522:Recombinases; D017422:Sequence Analysis, DNA; D013379:Substrate Specificity
chemical_list: D004269:DNA, Bacterial; D004278:DNA, Superhelical; D029968:Escherichia coli Proteins; D045522:Recombinases; C473360:XerC protein, E coli; D004254:DNA Nucleotidyltransferases; D019426:Integrases; C473361:XerD protein, E coli; C115006:integron integrase IntI1; D004264:DNA Topoisomerases, Type I