Abstract
The virulence plasmid of Salmonella enterica serovar Gallinarum-Pullorum (pSPV) but not those of Salmonella enterica serovars Enteritidis (pSEV) and Typhimurium (pSTV) can be readily mobilized by an F or F-like conjugative plasmid. To investigate the reason for the difference, the oriT-traM-traJ-traY-traA-traL regions of the three salmonella virulence plasmids (pSVs) were cloned and their nucleotide and deduced amino acid sequences were examined. The cloned fragments were generally mobilized more readily than the corresponding full-length pSVs, but the recombinant plasmid containing the oriT of pSPV was, as expected, more readily mobilized, with up to 100-fold higher frequency than the recombinant plasmids containing the oriT of the other two pSVs. The nucleotide sequences of the oriT-traM-traJ-traY-traA-traL region of pSEV and pSTV were almost identical (only 4 bp differences), but differed from that of pSPV. Major nucleotide sequence variations were found in traJ, traY, and the Tra protein binding sites sby and sbm. sby of pSPV showed higher similarity than that of pSEV or pSTV to that of the F plasmid. The reverse was true for sbm: similarity was higher with pSEV and pSTV than with pSPV. In the deduced amino acid sequences of the five Tra proteins, major differences were found in TraY: pSEV's TraY was 75 amino acids, pSTV's was 106 amino acids, and pSPV's was 133 amino acids; and there were duplicate consensus betaalphaalpha fragments in the TraY of pSPV and F plasmid, whereas there was only a single betaalphaalpha fragment in that of pSEV and pSTV.