Homologues of xerC/xerD genes have been found in many bacteria, and in the lactococci and streptococci, a single recombinase called XerS can perform the functions of XerC and XerD. The xerS gene of Streptococcus suis was cloned, overexpressed and purified as a maltose-binding protein (MBP) fusion. The purified MBP-XerS fusion showed specific DNA-binding activity to both halves of the dif site of S. suis, and covalent protein–DNA complexes were also detected with dif site suicide substrates. These substrates were also cleaved in a specific fashion by MBP-XerS, generating cleavage products separated by an 11-bp Obeticholic Acid order spacer region, unlike the traditional 6–8-bp spacer observed in most tyrosine recombinases. Furthermore, xerS mutants

of S. suis showed significant growth and morphological changes. The Xer site-specific recombination system is encoded by the circular chromosomes of many bacteria and functions to ensure that both INCB024360 circular

chromosomes and multicopy plasmids are monomeric before their segregation to daughter cells at cell division (Sherratt et al., 1995). The XerC/XerD proteins are tyrosine recombinases, which cooperatively bind to specific 11-bp consensus sequences that are separated by a 6- to 8-bp central region at the borders of which the DNA strands are cleaved and exchanged (Blakely et al., 1993). In recombination mediated by tyrosine recombinases, DNA strands are cleaved and rejoined through the formation of a transient DNA–protein covalent intermediate involving a conserved tyrosine as the catalytic nucleophile. To ensure that the correct order of strand exchanges occur at the right time and location, the dif site must be located at the terminus of the Escherichia coli chromosome and the C-terminal region of the FtsK protein is required to stimulate the strand exchange activity of XerD (Steiner et al., 1999; Barre et al., 2000; Yates et al., 2006). The translocation activity of FtsK is essential to make sure Staurosporine cell line that the products of the Xer recombination are unlinked and that chromosome dimer resolution can proceed successfully (Grainge et al., 2011). Recently, new studies have shown that a novel Xer recombination machinery

is present in Firmicutes, in some ε-proteobacteria and in the Archaea (Le Bourgeois et al., 2007; Carnoy & Roten, 2009; Cortez et al., 2010; Duggin et al., 2011). These bacteria possess only a single Xer protein that differs in primary sequence and in length with the other members of the XerCD family of recombinases. (Le Bourgeois et al., 2007). In the lactococci and streptococci, the binding and strand exchange activities of XerS are asymmetrical, with preferential binding to the left part of the difSL site and preferential exchange of the bottom strand (Nolivos et al., 2010). These authors suggest that FtsK may be needed to bring the dif sites together, but not to directly activate the strand exchange activity (Le Bourgeois et al., 2007; Nolivos et al., 2010).