PUTATIVE O-ANTIGEN TRANSPORT GENES WITHIN THE RFB REGION OF VIBRIO-CHOLERAE O1 ARE HOMOLOGOUS TO THOSE FOR CAPSULE TRANSPORT

The nucleotide sequence of that part of the Vibrio cholerae (Vc) O1 rf b region encompassing rfbG, rfbH and rfbI is presented. Expression of these genes has enabled the products for rfbG and rfbI to be confirmed , but the rfbH product has not been detected. Comparisons with the seq uences of known proteins reveals that RfbH and RfbI are likely to be i nvolved in the export of lipopolysaccharide (LPS). RfbH shows consider able homology to a number of integral membrane proteins, some of which have been identified as possibly having a role as an export channel f or capsular polysaccharides. RfbI corresponds to an ATP-binding protei n usually found linked to the membrane protein and is thought to be re quired for energizing this export process. Thus, we propose that RfbH and RfbI form a complex for the export of Vc O1 LPS. The function of R fbG is unknown, but it would appear to be a relatively hydrophilic pro tein and we can only speculate that it may be either a specific transf erase or possibly the O-antigen polymerase.