Nucleotide sequence of mkaD, a virulence-associated gene of Salmonella typhimurium containing variable and constant regions.

We have identified the nucleotide (nt) sequence of mkaD, a virulence-associated gene of the Salmonella typhimurium virulence plasmid, pEX102. The gene shows 98% homology on nt sequence level to mkfA, a corresponding gene of the S. typhimurium virulence plasmid pIP1350. The few nt changes, however, caused more extensive changes on the amino-acid level. The differences between mkaD and mkfA were clustered in distinct variable regions rather than being randomly scattered along the sequence. A third salmonellar virulence plasmid, pLT2, contained an mkaD gene identical to that of pEX102. Our observation suggests that the conserved virulence determinant on the plasmids of Salmonellae may contain different alleles of the same gene.