Next, we determined whether one, both, or neither of the putative RDFs uncovered by our bioinformatic analysis are required for VPI-2 excision. To do this, we constructed in-frame deletion mutations in each gene to create mutant selleck products strain SAM-3 (ΔvefA) and SAM-4 (ΔvefB). The two mutant strains and the wild-type N16961 were each inoculated into LB and all three strains grew similarly indicating that the mutant constructs did not have any general growth defect (data not shown). We determined the attB levels using QPCR in strain SAM-3
compared DMXAA to the wild-type strain grown under the same conditions. We found that no VPI-2 excision occurs in SAM-3 cells when compared with the wild type, indicating that a functional Trichostatin A copy of vefA is essential for efficient excision of VPI-2 (Figure 5). We complemented SAM-3 with a functional copy of vefA (SAM-5) and measured attB levels in these cells with the wild type levels both under standard conditions, to find that some excision occurred, but it was less than in wild-type cells (Figure 5). In our
vefB mutant strain (SAM-4), we found no difference in VPI-2 excision levels compared to wild-type grown under the same conditions, which demonstrates that vefB is not essential for excision (Figure 5). From these data it appears that vefA is the cognate RDF for VPI-2 excision. In our control experiments, transformation of SAM-3 with pBAD33 alone (resulting in strain SAM-13) did not affect attB levels (data not shown). Vibrio species island-encoded integrases with corresponding RDFs Given that our initial search for RDFs within one V. cholerae genome (strain N16961) yielded three putative RDFs (VC0497, VC1785, and VC1809), we decided to investigate further the occurrence of RDFs among Vibrio species whose genome sequence is available in the database. We performed BLAST searches against the 20 Vibrio species in the genome database, and we uncovered a total of 27 putative RDFs (Table
3). Next, we identified putative integrases within the genomes of the RDF homologues using BLAST GABA Receptor search analysis by using IntV2 as a seed. For each of the RDFs identified among the 27 genomes encompassing 10 different Vibrio species (V. cholerae, V. coralliilyticus, V. furnissii, V. harveyi, V. parahaemolyticus, V. splendidus, V. vulnificus, Vibrio sp. Ex25, RC341, and MED222), we identified a corresponding integrase with greater than 40% amino acid identities to IntV2 (VC1758) (Table 3). We examined the gene context of each RDF and integrase within each of the 20 strains to determine whether the RDF and integrase were located on the same region within a strain. From these analyses, we found that each of the 27 RDFs has a corresponding integrase within approximately 100 kb of each other (Table 3). It should be noted that from table 3, only three of the strains have been annotated completely and for many of the strains examined their ORF annotation numbering is not consecutive.