Phage Integrases for Genome Editing

Abstract

Phage integrases are prokaryotic site-specific recombinases that perform precise cut-and-paste recombination between their short attB and attP recognition sequences. These enzymes work in cellular environments ranging from bacteria to mammalian cells and have become useful genome engineering tools. PhiC31 was the first phage integrase to be developed for use in mammalian cells. This integrase has the useful property of being able to recombine its own attB and attP sites. In addition, phiC31 integrase performs recombination at related native sequences called pseudo att sites present in large genomes, which has allowed integration into unmodified genomes. PhiC31 integrase can also be used in conjunction with another phage integrase, Bxb1, which has different recognition sequences and does not recombine at pseudo att sites. The properties of these phage integrases have led to a range of applications, summarized here, from creation of transgenic organisms and in vivo gene therapy, to cellular reprogramming and precise genome editing by cassette exchange. The latest system, dual integrase cassette exchange (DICE), uses target phiC31 and Bxb1 attP sequences precisely placed in genomes by homologous recombination and is especially useful for iterative genome engineering in pluripotent stem cells.