title: Asymmetric DNA requirements in Xer recombination activation by FtsK.
abstract: In bacteria with circular chromosomes, homologous recombination events can lead to the formation of chromosome dimers. In Escherichia coli, chromosome dimers are resolved by the addition of a crossover by two tyrosine recombinases, XerC and XerD, at a specific site on the chromosome, dif. Recombination depends on a direct contact between XerD and a cell division protein, FtsK, which functions as a hexameric double stranded DNA translocase. Here, we have investigated how the structure and composition of DNA interferes with Xer recombination activation by FtsK. XerC and XerD each cleave a specific strand on dif, the top and bottom strand, respectively. We found that the integrity and nature of eight bottom-strand nucleotides and three top-strand nucleotides immediately adjacent to the XerD-binding site of dif are crucial for recombination. These nucleotides are probably not implicated in FtsK translocation since FtsK could translocate on single stranded DNA in both the 5'-3' and 3'-5' orientation along a few nucleotides. We propose that they are required to stabilize FtsK in the vicinity of dif for recombination to occur because the FtsK-XerD interaction is too transient or too weak in itself to allow for XerD catalysis.
authors.affiliation: CNRS, Centre de Génétique Moléculaire, FRE 3144, 91198 Gif-sur-Yvette, France.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Bonné
authors.forename: Sarah
authors.initials: S
authors.lastname: Bigot
authors.forename: Fabien
authors.initials: F
authors.lastname: Chevalier
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Allemand
authors.forename: François-Xavier
authors.initials: FX
authors.lastname: Barre
mesh_terms: D001483:Base Sequence; D004265:DNA Helicases / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry* / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000378:metabolism*; D019426:Integrases / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D009711:Nucleotides / Q000737:chemistry / Q000378:metabolism; D011995:Recombination, Genetic
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C096452:FtsK protein, E coli; D008565:Membrane Proteins; D009711:Nucleotides; C473360:XerC protein, E coli; D019426:Integrases; C473361:XerD protein, E coli; D004265:DNA Helicases