Identification of proteins expressed by the essential virulence region of the Salmonella dublin plasmid.

An 8 kilobase pair (kb) fragment from the Salmonella dublin 2229 plasmid is sufficient to restore virulence for mice to a cured strain of S. dublin. Deletion analysis of this virulence fragment identified at least one specific region required for virulence expression. Plasmid-directed protein synthesis in minicells has indicated the presence of at least four genes within the essential virulence region of the S. dublin plasmid, encoding proteins of 70, 33, 30 and 26 kDa. Analysis of the proteins expressed by the deletion derivatives suggested that expression of the 33 kDa polypeptide was linked to that of the 30 kDa polypeptide. The proteins expressed by the essential virulence region of the S. dublin plasmid appeared to be similar to the plasmid-encoded virulence proteins recently identified in S. typhimurium.