Site-specific recombination in mammalian cells expressing the Int recombinase of bacteriophage HK022

The int gene of bacteriophage HK022, coding for the integrase protein, was cloned in a mammalian expression vector downstream of the human cytomegalovirus (CMV) promoter. Green monkey kidney cells (COS-1) and mouse embryo fibroblast cells (NIH3T3) transiently transfected with the recombinant plasmid express the integrase protein. Co-transfection of this plasmid with reporter plasmids for site-specific recombination and PCR analyses show that the integrase promotes site-specific integration as well as excision. These reactions occurred without the need to supply integration host factor and excisionase, the accessory proteins that are required for integrase-promoted site-specific recombination in vitro as well as in the natural host Escherichia coli.