Xer recombinases are members of the tyrosine site-specific recombinase superfamily, a large group of enzymes that catalyze DNA breakage and rejoining using a conserved tyrosine nucleophile. Tyrosine recombinases promote various programmed DNA rearrangements including the monomerization of phage, plasmid and chromosome multimers, resolution of hairpin telomeres, and the movement of virulence and antibiotic resistance carrying integrative mobile genetic elements. Structural analysis of Helicobacter pylori XerH indicates that this N-terminal domain consisting of six alpha-helices contacts the DNA using a four-helix bundle [1].

1: Structural snapshots of Xer recombination reveal activation by synaptic complex remodeling and DNA bending. Bebel A, Karaca E, Kumar B, Stark WM, Barabas O; Elife. 2016; [Epub ahead of print] PMID:28009253