Identification of a Specific Pseudo attP Site for Phage PhiC31 Integrase in Bovine Genome

Background: PhiC31 integrase system provides a new platform in various felid of research, mainly in gene therapy and creation of transgenic animals. This system enables integration of exogenous DNA into preferred locations in mammalian genomes, which results in robust, long-term expression of the integrated transgene. Objectives: Identification of a novel pseudo attP site. Materials and Methods: Genomic DNA was extracted from primary bovine fetal fibroblast cells, which were stably transfected with EGFP and phiC31 integrase cDNAs carrying vectors. An inverse PCR was carried out for production of mini-circle DNAs and followed by sequencing. Results: A new specific pseudo attP site termed BF5 was identified in bovine genome.  This site is located in an intergenic AT rich region on chromosome 5 with similar features of other mammalian attP pseudo sites.  Furthermore, direct sequencing of generated attL site confirmed that site-specific transgene recombination was occurred at this site. Conclusions: This finding confirmed that phiC31 integrase could be feasible for production of transgenic animals for biotechnological applications.