DNA sequence and comparison of virulence plasmids from Rhodococcus equi ATCC 33701 and 103

The virulence plasmids of the equine virulent strains Rhodococcus equi ATCC 33701 and 103 were sequenced, and their genetic structure was analyzed, p3 3701 was 80,610 bp in length, and p103 was 1 bp shorter; their sequences we re virtually identical. The plasmids contained 64 open reading frames (ORFs ), 22 of which were homologous with genes of known function and 3 of which were homologous with putative genes of unknown function in other species. P utative functions were assigned to five ORFs based on protein family charac teristics. The most striking feature of the virulence plasmids was the pres ence of a 27,536-bp pathogenicity island containing seven virulence-associa ted protein (vap) genes, including vapA. These vap genes have extensive hom ology to vapA, which encodes a thermoregulated and surface expressed protei n. The pathogenicity island contained a LysR family transcriptional regulat or and a two-component response regulator upstream of six of the vap genes. The vap genes were present as a cluster of three (vapA, vapC, and vapD), a s a pair (vapE and vapF), or individually (vapG; vapH). A region of extensi ve direct repeats of unknown function, possibly associated with thermoregul ation, was present immediately upstream of the clustered and the paired gen es but not the individual vap genes. There was extensive homology among the C-terminal halves of all vap genes hut not generally among the N-terminal halves. The remainder of the plasmid consisted of a large region which ap p ears to be associated with conjugation functions and a large region which a ppears to be associated with replication and partitioning functions.