sentences:  The mechanism and control of serine recombinases is much less well understood.This group of enzymes was only discovered in the mid-1990s and is still relatively small.The now classical members gamma-delta and Tn3 resolvase, but also new additions like φC31-, Bxb1-, and R4 integrases, cut all four DNA strands simultaneously at points that are staggered by 2 bp (Fig.