Assembly of Eschenchia col: rfb gene products ; location and mechanisum

亚克隆、转座子插入和缺失分析表明，大肠杆菌09RFB区大小约为12kb。该区域至少编码7个多肽，分别为89、74、55、50、44、41和39.5千道尔顿。对以甘露糖均聚体为0的大肠杆菌08和09以及克雷伯氏菌03和05的RFB区的Southern杂交分析表明，E.coli09的RFB区由两个区域组成，这两个区域是所有这些RFB基因所共有的区域和特定的区域。中央特定区域两侧有两个公共区域。用鼠伤寒沙门氏菌的rfbK和rfbM对E.coli09 RFB突变进行了互补实验和酶活性的特异性试验，结果表明，该共同区域编码的50 kDa和55 kDa多肽分别为磷酸甘露糖变位酶和GDP-甘露糖焦磷酸化酶。该区域的核苷酸序列表明，与鼠伤寒沙门氏菌相同的功能基因存在rfbK和rfbM两个基因，rfbK和rfbM编码460个氨基酸(相对分子质量50,809)和471个氨基酸(相对分子质量52,789)的蛋白质。在鼠伤寒沙门氏菌的细菌甘露糖途径基因cpsB、铜绿假单胞菌的藻类、野油菜黄单胞菌的xanB以及沙门氏菌B、C、C2群的rfbM基因中，GDP-甘露糖焦磷酸化酶的氨基酸序列是保守的。根据氨基酸同源性，将其分为rfbK(09)型(rfbK(09)、rfbK(C1)、cpsg和Xana)、algC型和rfbK(B)型(rfbK(B)和rfbK(C2))。不能检测到这些组各自的磷酸甘露糖变位酶之间有显著的相似性。

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.