Flp Tyrosine-based site-specific recombinases (also called integrases), C-terminal catalytic domain.
Yeast Flp-like recombinases mediate the amplification of the 2 micron circular plasmid copy number by catalyzing the intra-molecular recombination between two inverted repeats during replication. They belong to the DNA breaking-rejoining enzyme superfamily, which also includes prokaryotic tyrosine recombinases and type IB topoisomerases. These enzymes share the same fold in their catalytic domain containing six conserved active site residues and the overall reaction mechanism. Flp-like recombinases are almost exclusively found in yeast and are highly diverged in sequence from the prokaryotic tyrosine recombinases. They cleave their target DNA in trans with a composite active site in which the catalytic tyrosine is provided by a promoter bound to a site other than the one being cleaved. Thus each active site within Flp complexes is assembled by domain swapping and contains catalytic residues from two different monomers. Two DNA segments are synapsed by the tetrameric enzyme, carrying the nucleophilic tyrosine in each active site with only two of the four monomers active at a given time. The catalytic domain is linked through a flexible loop to the N-terminal domain, which is largely responsible for non-specific DNA binding and isomerization. Its overall fold is similar to the SAM domain fold also found in the N-terminal domains of lambda integrase and XerD recombinase.