Highly efficient in vitro site-specific recombination system based on Streptomyces phage φBT1 integrase

The Streptomyces phage phi BT1 encodes a site-specific integrase of the large serine recombinase subfamily. In this report, the enzymatic activity of the phi BT1 integrase was characterized in vitro. We showed that this integrase has efficient integration activity with substrate DNAs containing attB and attP sites, independent of DNA supercoiling or cofactors. Both intra-and intermolecular recombinations proceed with rapid kinetics. The recombination is highly specific, and no reactions are observed between pairs of sites including attB and attL, attB and attR, attP and attL, or attP and attR or between two identical att sequences; however, a low but significant frequency of excision recombination between attL and attR is observed in the presence of the phi BT1 integrase alone. In addition, for efficient integration, the minimal sizes of attB and attP are 36 bp and 48 bp, respectively. This site-specific recombination system is efficient and simple to use; thus, it could have applications for the manipulation of DNA in vitro.