THE DNAK HOMOLOG OF THE MARINE VIBRIO SP STRAIN S14 BINDS TO THE UNPROCESSED FORM OF A CARBON STARVATION-SPECIFIC PERIPLASMIC PROTEIN

The Escherichia coli DnaK homologue in Vibrio sp. strain S14 was shown to possess chaperone function for translocation during carbon starvat ion. This was demonstrated by using the method of ca-immunoprecipitati on. DnaK co-precipitated with the carbon starvation-specific periplasm ic space protein Csp5 three hours after the onset of carbon starvation . Pulse-chasing of the protein with radiolabelled methionine followed by the addition of an excess of unlabelled methionine demonstrated tha t the Csp5 protein was translocated across the inner membrane. Only th e cytoplasmic unprocessed precursor form of Csp5 co-precipitated with DnaK. The non-covalent binding between the two proteins was found to b e ATP-dependent, as the addition of ATP released the interaction betwe en DnaK and the precursor form of Csp5, as was shown both on silver-st ained SDS-polyacrylamide gels and by Western blot analysis. We suggest that DnaK maintains the carbon starvation-inducible protein Csp5 in a translocation-competent form in the cytoplasm.