title: The unconventional Xer recombination machinery of Streptococci/Lactococci.
abstract: Homologous recombination between circular sister chromosomes during DNA replication in bacteria can generate chromosome dimers that must be resolved into monomers prior to cell division. In Escherichia coli, dimer resolution is achieved by site-specific recombination, Xer recombination, involving two paralogous tyrosine recombinases, XerC and XerD, and a 28-bp recombination site (dif) located at the junction of the two replication arms. Xer recombination is tightly controlled by the septal protein FtsK. XerCD recombinases and FtsK are found on most sequenced eubacterial genomes, suggesting that the Xer recombination system as described in E. coli is highly conserved among prokaryotes. We show here that Streptococci and Lactococci carry an alternative Xer recombination machinery, organized in a single recombination module. This corresponds to an atypical 31-bp recombination site (dif(SL)) associated with a dedicated tyrosine recombinase (XerS). In contrast to the E. coli Xer system, only a single recombinase is required to recombine dif(SL), suggesting a different mechanism in the recombination process. Despite this important difference, XerS can only perform efficient recombination when dif(SL) sites are located on chromosome dimers. Moreover, the XerS/dif(SL) recombination requires the streptococcal protein FtsK(SL), probably without the need for direct protein-protein interaction, which we demonstrated to be located at the division septum of Lactococcus lactis. Acquisition of the XerS recombination module can be considered as a landmark of the separation of Streptococci/Lactococci from other firmicutes and support the view that Xer recombination is a conserved cellular function in bacteria, but that can be achieved by functional analogs.
authors.affiliation: Laboratoire de Microbiologie et Génétique Microbienne, CNRS, Université Paul Sabatier, Toulouse, France. pascal.lebourgeois@ibcg.biotoul.fr
authors.forename: Pascal
authors.initials: P
authors.lastname: Le Bourgeois
authors.forename: Marie
authors.initials: M
authors.lastname: Bugarel
authors.forename: Nathalie
authors.initials: N
authors.lastname: Campo
authors.forename: Marie-Line
authors.initials: ML
authors.lastname: Daveran-Mingot
authors.forename: Jessica
authors.initials: J
authors.lastname: Labonté
authors.forename: Daniel
authors.initials: D
authors.lastname: Lanfranchi
authors.forename: Thomas
authors.initials: T
authors.lastname: Lautier
authors.forename: Carine
authors.initials: C
authors.lastname: Pagès
authors.forename: Paul
authors.initials: P
authors.lastname: Ritzenthaler
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D002876:Chromosomes, Bacterial / Q000235:genetics / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D023281:Genomics; D019426:Integrases / Q000235:genetics / Q000378:metabolism; D017045:Lactococcus / Q000235:genetics* / Q000378:metabolism*; D013294:Lactococcus lactis / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010802:Phylogeny; D045522:Recombinases / Q000235:genetics* / Q000378:metabolism*; D011995:Recombination, Genetic; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D013291:Streptococcus / Q000235:genetics* / Q000378:metabolism*; D013296:Streptococcus pneumoniae / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D045522:Recombinases; D019426:Integrases