GENETIC ORGANIZATION AND EVOLUTION OF YERSINIA-PSEUDOTUBERCULOSIS 3,6-DIDEOXYHEXOSE BIOSYNTHETIC GENES

3,6-dideoxyhexose (DDH) sugars occur in some of the O antigens of Salm onella enterica and Yersinia pseudotuberculosis, but are otherwise rar ely found in nature. Y. pseudotuberculosis DDH biosynthetic genes rfbS (encoding CDP-paratose synthetase) and rfbE (encoding CDP-tyvelose ep imerase) were amplified and cloned, and their sequences determined. Co mparisons with the equivalent genes of S. enterica show that the genet ic arrangement of DDH genes is very similar; however, in Y. pseudotube rculosis there is no suggestion that paratose producing strains are de rived from tyvelose-producing strains by inactivation of rfbE, which i s the case in S. enterica. The previously determined DNA sequence of t he rfb region of an abequose-producing strain was re-examined. It cont ains the remnants of an insertion sequence (IS) adjacent to a truncate d acid non-functional rfbE gene. This suggests that the IS was involve d in recombination events contributing to O-antigen antigenic diversit y in Y. pseudotuberculosis.