Integrative module of the high-pathogenicity island of Yersinia

The high-pathogenicity island of Yersinia pestis (Yps HPI) encodes virulenc e-associated genes involved in siderophore yersiniabactin-mediated iron upt ake. The Yps HPI contains a P4-type integrase (Int-HPI), associated with th e asn-tRNA locus, and is flanked by 17 bp direct repeats. We constructed a minimal integrative module of the pathogenicity island carrying the reconst ituted 266 bp attP (POP') attachment site derived from putative attR and at tL junctions of the Yps HPI and the functional int-HPI gene from Y. pestis KUMA. The attP-int-HPI module recombined efficiently, site specifically and RecA independently with the bacterial attB site present either in the chro mosome (asn-tDNA) or on a plasmid, with no preference for a certain asn-tRN A gene. The excision of the integrated suicide plasmid carrying the integra tive module, on the other hand, was a rare event and could be demonstrated only by polymerase chain reaction. Analysis of the 5' terminus of the trans cript for int-HPI revealed that the integration of attP-int-HPI was coupled with the replacement of the endogenous int-HPI promoter, localized in the P' part of the attP site, by the adjacent asn-tRNA promoter. These results suggest that two alternative promoters control integration and excision of the HPI by its integrase.