The Cre/loxP recombination system

Abstract

Abstract The Pl bacteriophage Cre recombinase recognizes and mediates site-specific recombination between 34 bp sequences referred to as loxP (locus of crossover (x) in Pl) (35). The loxP sequence consists of two 13 bp inverted repeats interrupted by an 8 bp nonpalindromic sequence which dictates the orientation of the overall sequence (Figure 3a) (36, 37). When two loxP sites are placed in the same orientation on a linear DNA molecule, a Cre-mediated intramolecular recombination event results in the excision of the loxP-flanked, or ‘floxed’, sequence as a circular molecule with one loxP site left on each reaction product (Figure 3b). The reverse reaction, an intermolecular recombination event, will result in the integration of the circular DNA molecule into the linear molecule, each possessing one loxP site. Alternatively, an intermolecular recombination event between two linear molecules as substrates (again, each possessing one loxP site) results in the reciprocal exchange of the regions flanking the loxP sites (Figure 3c). If the two loxP sites are placed in opposing orientation the floxed sequence will be inverted (Figure 3d) (38-40).