Identification of a multimer resolution system involved in stabilization of the Salmonella dublin virulence plasmid pSDL2.
The Salmonella dublin virulence plasmid pSDL2 is a low-copy-number plasmid that is highly conserved in its host. Deletion of the 8-kb EcoRI C fragment downstream of the virulence region leads to plasmid instability and formation of multimers. We identified a multimer resolution system in the EcoRI C fragment composed of a trans-acting resolvase gene and a cis-acting resolution site. The resolvase gene, rsd, maps within a 2-kb EcoRV fragment and appears to be part of a multicistronic unit together with at least two other genes of unknown function. The derived protein, 28.7-kDa in size, is almost identical to the D protein of miniF. The C-terminal region was shown to have substantial similarity to the conserved C-terminal domains of the site-specific recombinases of the integrase family. The cis-acting resolution site, crs, is located upstream of rsd within a 628-bp SmaI-HpaI fragment. It contains eight direct incomplete 17-bp repeats followed by a segment rich in indirect repeats, the latter being homologous to the oriV1 sequence of miniF. crs contains the crossover site for specific recombination and mediates bidirectional promoter activity. A replicative function in analogy to that of oriV1 of F could not be demonstrated. The multimer resolution system was shown to stabilize pACYC184 and is dependent on the recA-mediated formation of multimeric plasmids. Screening different Salmonella serovars with a pSDL2-specific recombination assay revealed that only strains harboring a virulence plasmid encode for resolvase activity. Our results suggest that site-specific recombination contributes to the stable inheritance of pSDL2 and other Salmonella virulence plasmids.
Krause
M
M
Department of Medicine, University of California, San Diego 92103.
Guiney
D G
DG
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009713:Nucleotidyltransferases / Q000737:chemistry / Q000235:genetics*; D010957:Plasmids; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D012475:Salmonella / Q000235:genetics / Q000472:pathogenicity*; D019895:Transposases
D004269:DNA, Bacterial; D009713:Nucleotidyltransferases; D019895:Transposases