Identification and sequence of rfbS and rfbE, which determine antigenic specificity of group A and group D salmonellae.
Salmonella group A, group B, and group D strains have paratose, abequose, and tyvelose, respectively, as the immunodominant sugar in their O antigens, which are otherwise identical; only the final steps differ in the biosynthetic pathways of these sugars. The gene rfbJ from a group B strain, encoding abequose synthase, the final and only unique step in the biosynthesis of CDP-abequose, has been cloned and sequenced (P. Wyk and P. Reeves, J. Bacteriol. 171:5687-5693, 1989). In this study, we locate and sequence rfbS and rfbE from serovars typhi and paratyphi, representative of groups A and D. Gene rfbS is present in both groups and encodes paratose synthase, which carries out a step parallel to that of abequose synthase, but the product is CDP-paratose. The DNA and inferred amino acid sequences are compared with those of rfbJ. We conclude that the genes are homologous, but the divergence is extremely ancient. Gene rfbE encodes CDP-tyvelose epimerase, which converts CDP-paratose to CDP-tyvelose in group D strains; the gene is active in group D strains, and we find it to be present in a mutant form in group A strains. These two genes encode the steps unique to groups A and D and, like rfbJ of group B, are of low G+C content, suggesting transfer from outside of salmonellae. The evolutionary origin of these genes is discussed.
Verma
N
N
Department of Microbiology, University of Sydney NSW, Australia.
Reeves
P
P
D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000235:genetics*; D001483:Base Sequence; D005075:Biological Evolution; D015139:Blotting, Southern; D002238:Carbohydrate Epimerases / Q000235:genetics*; D003001:Cloning, Molecular; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics*; D011135:Polysaccharides, Bacterial / Q000235:genetics*; D011994:Recombinant Proteins / Q000096:biosynthesis; D012485:Salmonella typhi / Q000235:genetics*; D013045:Species Specificity; D000637:Transaminases
D000942:Antigens, Bacterial; D011135:Polysaccharides, Bacterial; D011994:Recombinant Proteins; D010088:Oxidoreductases; D000637:Transaminases; D002238:Carbohydrate Epimerases; C061271:paratose synthase; C061272:perosamine synthetase