(2) Retroviral integrase domains The tyrosine-type site-specific recombinase core-binding (CB) (IPR044068) is involved in a number of important gene rearrangement reactions. In addition to its involvement in protein-protein interactions, it primarily interacts with the primary groove of the attachment site, facilitating binding to the core DNA sequence. Some recombinases, like lambda Int and IntDOT, have an extra amino-terminal domain that helps them find arm sites, which are on both sides of the crossover region, and tells the recombination reaction which way to go.