Cre Recombinase - Discovery

Discovery

Studies carried out in 1981 by Sternberg & Hamilton demonstrated that the bacteriophage P1 had a unique site specific recombination system. EcoRI fragments of the P1 Bacteriophage genome were generated and cloned into lambda vectors. A 6.5x103 base EcoRI fragment (Fragment 7) was found to permit efficient recombination events. The mechanism of these recombination events was known to be unique as they occurred in the absence of bacterial RecA and RecBCD proteins. The components of this recombination system were elucidated using deletion mutagenesis studies. These studies showed that a P1gene product and a recombination site were both required for efficient recombination events to occur. The P1 gene product was named Cre (Causes Recombination) and the recombination site was named loxP (locus of crossing (x) over,P1). The Cre protein was purified in 1983 and was found to be a 35,000 Da protein. It was also elucidated at this time that no high energy cofactors such as ATP or accessory proteins are required for the recombinase activity of the purified protein. Early studies also demonstrated that Cre binds to non specific DNA sequences whilst having a 20 fold higher affinity for loxP sequences and results of early DNA footprinting studies also suggested that Cre molecules bind loxP sites as dimers.