A MOLECULAR CHAPERONE, CLPA, FUNCTIONS LIKE DNAK AND DNAJ

The two major molecular chaperone families that mediate ATP-dependent protein folding and refolding are the heat shock proteins Hsp60s (GroE L) and Hsp70s (DnaK). Clp proteins, like chaperones, are highly conser ved, present in all organisms, and contain ATP and polypeptide binding sites. We discovered that ClpA, the ATPase component of the ATP-depen dent ClpAP protease, is a molecular chaperone. ClpA performs the ATP-d ependent chaperone function of DnaK and DnaJ in the in vitro activatio n of the plasmid P1 RepA replication initiator protein. RepA is activa ted by the conversion of dimers to monomers. We show that ClpA targets RepA for degradation by ClpP, demonstrating a direct link between the protein unfolding function of chaperones and proteolysis. In another chaperone assay, ClpA protects luciferase from irreversible heat inact ivation but is unable to reactivate luciferase.