Phage Bxb1 Integrase Mediates Highly Efficient Site-Specific Recombination in Mammalian Cells

Mammalian Markup Recombination techniques utilizing the Cre and Flp systems are now accepted as standard procedures in genome engineering, particularly in manipulating embryonic stem cells, replacing less flexible restriction enzyme approaches. Notwithstanding their popularity, the frequently lackluster efficiency of integration/recombination is still a confounding factor with these approaches. The use of phage-derived serine recombinases has been an attractive alternative to Cre/Flp tyrosine recombinases, but their frequent requirement for cofac-tors and poor efficacy has reduced their appeal. The Bxb1 integrase, however, has recently proven its worth as a robust serine recombinase that is active with fewer restrictions than other such integrases. In the article on p. 460 of this issue, Russell et al. describe for the first time the use of a codon-optimized Bxb1 integrase in mammalian cells, showing that it is able to catalyze unidirectional recombination between attP and attB sites with high efficiency....