MOLECULAR AND FUNCTIONAL-ANALYSIS OF GENES REQUIRED FOR EXPRESSION OFGROUP-IB K-ANTIGENS IN ESCHERICHIA-COLI - CHARACTERIZATION OF THE HIS-REGION CONTAINING GENE CLUSTERS FOR MULTIPLE CELL-SURFACE POLYSACCHARIDES

Escherichia coil group I capsular K antigens are found in two forms on the cell surface. The K-LPS form is linked to lipopolysaccharide lipi d A core, whereas the high-molecular-weight capsular form is assembled independently of lipid A core. Subgroup IB K antigens are generally c o-expressed with either the O8 or O9 antigen and, under the appropriat e conditions, with the exopolysaccharide, colanic acid. To examine the relationships between the genetic loci and the synthetic pathways for these various cell-surface polymers, the gene cluster responsible for expression of a prototype group IB K antigen (serotype K40) was clone d and the flanking chromosomal regions characterized. Analysis of the six orfs within the cluster indicates features typical of Wzy (Rfc)-de pendent O antigens. Synthesis of group IB K antigens is initiated by W ecA (Rfe), a UDP-GlcNAc::undecaprenylphosphate GlcNAc-1-phosphate tran sferase, and the chain length of K40(LPS) is determined by the wzz gen e product. The his-region of the E. coil O8:K40 prototype is almost ex clusively devoted to the expression of three different surface polysac charides. The rfb(K40) cluster is located adjacent to the cps (colanic acid synthesis) and rfb(O8) (O8 antigen synthesis) loci in the gene o rder: his-rfb(O8/O9)-wzz-ugd-gnd-rfb(K40)-galF-cps. Thus, rfb(K40) is in the location occupied by other Wzy-dependent rfb gene dusters, and rfb(O8/O9) represents an additional locus.