The attP(TP901-1) site (5'-TCCAACTCGCTTAATTGCGAGTTTTTATTTCGTTTATTtcaatTAAGGTAACTAAA-3') is one of the two target sites of the TP901-1:int integrase. TP901-1:int mediates recombination between two non-identical target sites, attP(TP901-1) and attB(TP901-1), each of which contains a short integration core flanked by imperfect inverted repeats. Exchange between the attP(TP901-1)/attB(TP901-1) pair results in the formation of hybrid sites that are no longer a substrate of the TP901-1:int integrase, and thus the exchange reaction driven by TP901-1:int is unidirectional (PMID:11495984). The recombination event catalyzed by TP901-1:int results in genetic modification, the nature of which is influenced by the relative orientation (direct or inverted), and location of the two target sites. The types of possible modification include deletion of DNA, generation of chromosomal rearrangements and integration of DNA into the genome (PMID:16981199).