DISTRIBUTION OF THE ROL GENE ENCODING THE REGULATOR OF LIPOPOLYSACCHARIDE O-CHAIN LENGTH IN ESCHERICHIA-COLI AND ITS INFLUENCE ON THE EXPRESSION OF GROUP-I CAPSULAR K ANTIGENS

The rol (cld) gene encodes a protein involved in the expression of lip opolysaccharides in some members of the family Enterobacteriaceae. Rol interacts with one or more components of Rfc-dependent O-antigen bios ynthetic complexes to regulate the chain length of lipopolysaccharide O antigens, The Rfc-Rol-dependent pathway for O-antigen synthesis is f ound in strains with heteropolysaccharide O antigens, and, consistent with this association, rol-homologous sequences were detected in chrom osomal DNAs from 17 different serotypes with heteropolysaccharide O an tigens. Homopolymer O antigens are synthesized by a pathway that does not involve either Rfc or Rol, It was therefore unexpected when a surv ey of Escherichia coli strains possessing mannose homopolymer O8 and O 9 antigens showed that some strains contained rol. All 11 vol-positive strains coexpressed a group IB capsular K antigen with the O8 or O9 a ntigen, In contrast, 12 vol-negative strains all produced group ZA K a ntigens in addition to the homopolymer O antigen, Previous research fr om this and other laboratories has shown that portions of the group I K antigens are attached to lipopolysaccharide lipid A-core, in a form that we have designated K-LPS. By constructing a hybrid strain with a deep rough rfa defect, it was shown that the K40 (group IB) K-LPS anti gen exists primarily as long chains, However, a significant amount of K49 antigen was surface expressed in a lipid A-core-independent pathwa y, The typical chain length distribution of the K40 antigen was altere d by introduction of multicopy vol, suggesting that the K40 group IB K antigen is equivalent to a Rol dependent O antigen, The prototype K30 (group IA) K antigen is expressed as short oligosaccharides (primaril y single repeat units) in K-LPS, as well as a high-molecular-weight li pid A-core-independent fhigh-molecular-weight lipid A-core-independent form, Introduction of multicopy rol into the K30 strain generated a n ovel modal pattern of K-LPS with longer polysaccharide chains. Collect ively, these results suggested that group IA K-LPS is also synthesized by a Rol-dependent pathway and that the typically short oligosacchari de K-LPS results from the absence of Rol activity in these strains.