Hsc62, a new DnaK homologue of Escherichia coli

We have cloned and expressed the ORF o170#1 of Escherichia coli, which encodes a 62-kDa protein sharing 33% homology in primary structure with DnaK and Hsc66, Hsp70 homologues of E. coli. The purified gene product, which we named Hsc62, clearly showed ATPase activity and was bound to a gelatin-agarose gel, from which it was specifically eluted with ATP magnesium salt. Thus, Hsc62 is similar to DnaK in this respect and probably functions as a molecular chaperon in E. coli. However, Hsc62 differs markedly from DnaK and also from Hsc66 in response to temperature: the optimum temperature for ATPase activity was increased stepwise in the order of Hsc62, Hsc66, and DnaK. Hsc66 is activated by DnaJ of E. coli in the same manner as DnaK, the natural partner protein of DnaJ. However, Hsc62 is distinct from the others: the ATPase activity of Hsc62 was not elevated by DnaJ.