The E. coli dnaK gene product, the hsp70 homolog, can reactivate heat-inactivated RNA polymerase in an ATP hydrolysis-dependent manner.

Pelham previously proposed that the hsp70 family of heat shock proteins could prevent the formation and/or allow the dissolution of protein aggregates created during stress conditions. We confirmed this hypothesis by showing that the E. coli hsp70 homolog, the dnaK gene product, protects the host RNA polymerase enzyme from heat inactivation in an ATP-independent reaction. In addition, we show that heat-inactivated and aggregated RNA polymerase is both disaggregated and reactivated following simultaneous incubation with DnaK protein and hydrolyzable ATP. The DnaK756 mutant protein has lost the ability to disaggregate the inactivated RNA polymerase enzyme. Our results demonstrate that the DnaK protein contributes to E. coli's growth not only by protecting some enzymes from denaturation but also by reactivating some once they are misfolded or aggregated.