Cooperates with DnaJ, GrpE and ClpB to reactivate heat-inactivated proteins. Forms a heterononamer with DnaJ and DafA in the resting state. Three copies of each protein are present in the complex. By stress conditions e.g. heat shock (By similarity). In the resting state, the DnaK-DnaJ-DafA complex cannot bind substrate. As the substrate becomes sufficiently high, DafA is displaced and an active DnaK-substrate-DnaJ complex is formed. Belongs to the heat shock protein 70 family.