Molecular analysis of the 3,6-dideoxyhexose pathway genes of Yersinia pseudotuberculosis serogroup IIa

Salmonella enterica and Yersinia pseudotuberculosis are the only examples in nature known to use a variety of 3,6-dideoxyhexose derivatives as 0 antigen constituents. To allow a comparison of the responsible biosynthetic genes ofthe two organisms, we have sequenced a section of the Y. pseudotuberculosis serogroup IIA rfb region that contained the genes for the abequose biosynthetic pathway. Comparison of the identified genes with the rib region of S. enterica LT2 showed that the two dideoxyhexose pathway gene clusters are related. The arrangement of the genes was largely conserved, and the G+C compositions of the two DNA regions were strikingly similar; however, the degree of conservation of nucleotide and protein sequences suggested that the two gene clusters have been evolving independently for considerable time. Hybridization experiments showed that the dideoxyhexose pathway genes are widespread throughout the various serogroups of Y. pseudotuberculosis. 3,6-Dideoxyhexoses (DDH) are a group of unusual, highly immunodominant monosaccharides found almost exclu-sively within the 0 antigen component of lipopolysaccharide (LPS). Of eight possible derivatives, only five have so far been found to occur naturally: four of them (abequose