Site-specific and directional gene replacement mediated by Cre recombinase

A novel method for the site-specific introduction of genes into eukaryotic cells using the prokaryotic Cre-LoxP recombination system is presented. Cre recombinase catalyzes recombination between two LoxP sites or between two mutant LoxP 511 sites. However, recombination is not catalyzed between a LoxP and a LoxP 511 site. We now demonstrate that it is possible to catalyze accurate exchange between two DNA segments each flanked by a LoxP and a LoxP 511 site. In the example presented, expression of the Cre recombinase resulted in the replacement of a murine IgA constant region gene with a LoxP site at the 5' end and a LoxP 511 site at the 3' end by a human IgA constant region gene flanked by the same wild type and mutant LoxP sites. This method provides a novel approach for the site-specific substitution of specific genes.