EXPRESSION OF THE O-ANTIGEN GENE-CLUSTER IS REGULATED BY RFAH THROUGHTHE JUMPSTART SEQUENCE

O antigen genes are clustered, with a JUMPstart sequence located upstr eam. JUMPstart is a 39-bp sequence, present upstream of many polysacch aride gene clusters and also upstream of haemolysin and F factor gene clusters. RfaH is known to regulate the expression of E. coli group II capsule, haemolysin, F factor and the outer core of lipopolysaccharid e all of which have the JUMPstart sequence. and has been shown to func tion as a transcriptional antiterminator in some cases. Using lacZ Fus ions to genes in the O antigen gene cluster of Salmonella enterica ser ovar Typhimurium, we found that RfaH also regulates the expression of O antigen. We showed that RfaH enhances expression of the 18-kb O anti gen gene cluster, with promoter-distal genes affected more dramaticall y. We also showed that the JUMPstart sequence was required for RfaH fu nction. (C) 1998 Federation of European Microbiological Societies. Pub lished by Elsevier Science B.V. All rights reserved.