POINT MUTATIONS IN THE TRANSMEMBRANE DOMAIN OF DJLA, A MEMBRANE-LINKED DNAJ-LIKE PROTEIN, ABOLISH ITS FUNCTION IN PROMOTING COLANIC ACID PRODUCTION VIA THE RCS SIGNAL-TRANSDUCTION PATHWAY

DjlA is a novel DnaJ-like protein localized to the inner membrane of E scherichia coli through the single transmembrane domain (TMD) found at the N-terminus. The overproduction of DjlA activates expression of th e cps operon, controlling synthesis and export of the extracellular po lysaccharide colanic acid via the Rcs/B two-component signal transduct ion pathway. We now show that both the TMD and the J-region are essent ial for the induction of cps expression observed with the overproducti on of DjlA. Furthermore, we describe the isolation and characterizatio n of different point mutations in the TMD that completely or partially block the induction of cps expression associated with overproduction of DjlA. These mutations were shown not to affect the localization, st ability or topology of the mutant DjlA proteins. We propose that these mutations are affecting specific interactions between the TMD of DjlA and its substrate protein(s), for example RcsC, the membrane sensor k inase partner of the Rcs/B signal transduction pathway.