POSITIVE CONTROL OF THE 2-COMPONENT RCSC B SIGNAL-TRANSDUCTION NETWORK BY DJLA - A MEMBER OF THE DNAJ FAMILY OF MOLECULAR CHAPERONES IN ESCHERICHIA-COLI/

The membrane-anchored DjlA protein represents the third member of the DnaJ 'J-domain' family of Escherichia coli that includes DnaJ and CbpA . DjlA possesses a J-domain at its extreme C-terminus but shares no ad ditional homology with DnaJ, Our genetic analysis suggests that DjlA a cts in concert with the RcsB/C two-component signal transduction syste m to augment induction of the cps (capsular polysaccharide) operon and synthesis of colanic acid mucoid capsule. The DjlA J-domain is essent ial for the observed stimulation of this pathway as deletion, or intro duction of the mutation H233Q, within the highly conserved HPD tripept ide abolished all inducing activity. Deletion of the transmembrane anc hor sequence also abolished all inducing activity, djlA is not an esse ntial gene under all conditions tested, nor is it essential for mucoid capsule biosynthesis; however, strong overexpression leads to rapid l oss of cell viability suggesting that the gene is normally tightly reg ulated. Northern analysis revealed that djlA message was extremely uns table but could be induced or stabilized in response to cold shock. Th e activation of the cps operon by DjlA is dependent upon both DnaK(Hsp 70) and GrpE, and therefore we propose a role for DjlA, together with this chaperone machine, as a novel regulator of a two-component histid ine kinase signal transduction pathway.