Recombinase

Site specific recombinases

These enzymes, derived from bacteria (bacteriophages) and fungi, catalyze directionally sensitive DNA exchange reactions between short target site sequences specific to each recombinase. The reactions enable excision/insertion, inversion, translocation, and cassette exchange. Examples include Cre, Hin, Tre, and FLP recombinases. They are widely used in multicellular organisms to manipulate genome structure and control gene expression.

Homologous recombination

Recombinases central to homologous recombination occur in archaea, bacteria, eukaryotes, and viruses. The archaeon Sulfolobus solfataricus RadA recombinase catalyzes DNA pairing and strand exchange, key steps in recombinational repair; RadA is more similar to eukaryotic Rad51 than to bacterial RecA. RecA recombinase, universally present in bacteria, functions in DNA repair, including repair of stalled replication forks and natural genetic transformation. Eukaryotic Rad51 and its family members are homologous to archaeal RadA and bacterial RecA; Rad51 is highly conserved from yeast to humans and is key in recombinational repair of DNA damages, especially double-strand breaks.

Over- or under-expression of human Rad51 occurs in many cancers. During meiosis, Rad51 interacts with Dmc1, another recombinase homologous to RecA, to form a presynaptic filament; Dmc1 function appears limited to meiotic recombination. Some DNA viruses encode recombinases such as bacteriophage T4 UvsX, homologous to RecA, which facilitates assimilation of linear single-stranded DNA into a homologous DNA duplex to form a D-loop.