| Research Abstract |
Subcloning, transposon insertion, and deletion analyses reveal that Escherichia coli 09 rfb region is about 12 Kilobase pairs. The region encodes at least seven polypeptides of 89, 74, 55, 50, 44, 41, and 39.5 kilodaltons. Southern hybridization analysis of rfb regions of Escherichia coli 08 and 09, and Klebsiella 03 and 05, which have mannose homopolymers as their 0 polysaccharides, shows that the E.coli 09 rfb region consists of two regions, common to all these rfb genes and the specific region. The central specific region is flanked by two common regions. Complementation experiments of E.coli 09 rfb mutations with rfbK and rfbM of Salmonella typhimurium and the specific tests for the enzymatic activity show that the 50 and 55 kDa polypeptides, encoded by the common region, are phosphomannomutase and GDP-mannose pyrophosphorylase, respectively. Nucleotide sequence of the region reveals the presence of two genes, rfbK and rfbM, with respect to the same functional genes of S. typhimurium.rfbK and rfbM encode proteins of 460 amino acids (molecular weight of 50,809) and 471 amino acids (molecular weight of 52,789). The amino acid sequences of GDP-mannose pyrophosphorylase were conserved in the bacterial mannose pathway genes of cpsB of S. typhimurium, algA of Pseudomonas aeruginosa, xanB of Xanthomonas campestris, and rfbM genes of Salmonella group B, C1, and C2. From the data of amino acid identities of phosphomannomutase genes, they were classified into three groups of rfbK(09) type (rfbK(09), rfbK(C1), cpsG, and xanA), algC type, and rfbK(B)type (rfbK(B) and rfbK(C2). No striking similarity among these groups of the respective phosphomannomutase could be detected.
|
