PMID:17630835

Citation	Le Bourgeois, P, Bugarel, M, Campo, N, Daveran-Mingot, ML, Labonté, J, Lanfranchi, D, Lautier, T, Pagès, C and Ritzenthaler, P (2007) The unconventional Xer recombination machinery of Streptococci/Lactococci. PLoS Genet. 3:e117
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.
Links	PubMed PMC1914069 Online version:10.1371/journal.pgen.0030117
Keywords	Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Base Sequence; Chromosomes, Bacterial/genetics; Chromosomes, Bacterial/metabolism; DNA, Bacterial/genetics; Escherichia coli/genetics; Escherichia coli/metabolism; Genomics; Integrases/genetics; Integrases/metabolism; Lactococcus/genetics; Lactococcus/metabolism; Lactococcus lactis/genetics; Lactococcus lactis/metabolism; Molecular Sequence Data; Mutagenesis; Phylogeny; Recombinases/genetics; Recombinases/metabolism; Recombination, Genetic; Sequence Homology, Nucleic Acid; Species Specificity; Streptococcus/genetics; Streptococcus/metabolism; Streptococcus pneumoniae/genetics; Streptococcus pneumoniae/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
LACLM:XERS		GO:0009037: tyrosine-based site-specific recombinase activity	ECO:0000315:		F		IMP was conclude based on Figure 3, which indicates XerS/difSL Recombination in E. coli. In absence of the lactococcal XerS recombinase, almost no recombination was observed indicating that XerCD of E. coli do not recombine difSL. In contrast, introduction of a plasmid expressing the lactococcal xerS gene increased the excision frequency (observed in E. coli when using the native XerCD/dif system.)	complete CACAO 4166
LACLM:XERS	enables	GO:0009037: tyrosine-based site-specific recombinase activity	ECO:0000315: mutant phenotype evidence used in manual assertion		F		Seeded From UniProt	complete

References

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