The role of Caulobacter crescentus XerC and XerD recombinases in site-specific recombination
In most bacteria, the chromosomal dimer resolution process is mediated by two tyrosine recombinases, XerC and XerD, which bind cooperatively and perform the recombination reaction at the dif site near the terminus of replication.  This reaction also requires the C-terminal domain of the cell division protein FtsK. Caulobacter crescentus is an aquatic Gram-negative bacterium found in various environments. This bacterium has an asymmetric cell cycle which can be used to synchronize cell growth in order to study the temporal expression of a gene and the interconnection between the cell cycle and development. The binding activity and the formation of phosphotyrosyl complex of the C. crescentus recombinases, ccXerC and ccXerD, were tested on the C. crescentus dif (ccdif) site. Both ccXerC and ccXerD bound preferentially to the left half-site of ccdif and showed reduced cooperative binding, unlike what was found with the E. coli dif site. Covalent complex formation activity was tested by using fluorescently labelled linear “nicked suicide substrates” and labelled proteins. Heat and SDS-resistant protein-DNA complexes were formed when both wild-type ccXerC and ccXerD reacted with ccdif but not in the presence of active-site tyrosine mutant proteins. Phosphotyrosine complexes formed on the top-nicked suicide substrate were found to be more efficient than on the bottom-nicked suicide substrates and surprisingly ccXerC remained bound to both top and bottom-nicked ccdif suicide substrates.
Tyrosine recombinase XerC XerD dif Caulobacter crescentus Site-specific recombination Tyrosine recombinase XerC XerD dif Caulobacter crescentus