CRYSTAL-STRUCTURE OF THE SITE-SPECIFIC RECOMBINASE, XERD

The structure of the site-specific recombinase, XerD, that functions i n circular chromosome separation, has been solved at 2.5 Angstrom reso lution and reveals that the protein comprises two domains, The C-termi nal domain contains two conserved sequence moths that are located in s imilar positions in the structures of XerD, lambda and HP1 integrases. However, the extreme C-terminal regions of the three proteins, contai ning the active site tyrosine, are very different, In XerD, the arrang ement of active site residues supports a cis cleavage mechanism, Bioch emical evidence for DNA bending is encompassed in a model that accommo dates extensive biochemical and genetic data, and in which the DNA is wrapped around an alpha-helix in a manner similar to that observed for CAP complexed with DNA.