Specific stimulation of human apurinic/apyrimidinic endonuclease by heat shock protein 70

We previously demonstrated the stimulation of human apurinic/apyrimidinic endonuclease 1 (HAP1) by heat shock protein 70 (HSP70). In this work, we further defined the functional interaction between these proteins. Digestion of HSP70 by trypsin released 48 and 43 kDa amino terminal fragments that retained the ability to stimulate HAP1. In agreement with this result, an HSP70 N-terminal deletion mutant protein containing amino acids 1–385 was comparable to the full-length protein in its ability to enhance HAP1 activity. HSP70 mutants containing carboxy terminal amino acids 386–640 stimulated HAP1 only slightly, as did unrelated proteins. These results implicate the amino terminal portion of HSP70 in stimulating the activity of HAP1.