Figure 1.

The ΦC31 Int system can also be used for mammalian genome modification, especially in basic research of gene therapy. In the presence of this Int, without host factors, the integration reaction mediates recombination between a short sequence of mammalian genome DNA, the pseudo attachment site-attP, and a short sequence in extrinsic DNA vectors, the attachment site-attB. The extrinsic gene integrates into the mammalian chromosome where it is flanked by two hybrid att sites, attL and attR. Once the integration occurs, the extrinsic genes can be stably integrated into the host genome with high efficiency.