THE DNAJ CHAPERONE CATALYTICALLY ACTIVATES THE DNAK CHAPERONE TO PREFERENTIALLY BIND THE SIGMA(32) HEAT-SHOCK TRANSCRIPTIONAL REGULATOR

In Escherichia coli the heat shock response is under the positive control of the sigma(32) transcription factor. Three of the heat shock proteins, DnaK, DnaI, and GrpE, play a central role in the negative autoregulation of this response at the transcriptional level. Recently, we have shown that the DnaK and DnaJ proteins can compete with RNA polymerase for binding to the sigma(32) transcription factor in the presence of ATP, by forming a stable DnaJ-sigma(32)-DnaK protein complex. Here, we report that DnaJ protein can catalytically activate DnaK's ATPase activity. In addition, DnaJ can activate DnaK to bind to sigma(32) in an ATP-dependent reaction, forming a stable sigma(32)-DnaK complex. Results obtained with two DnaJ mutants, a missense and a truncated version, suggest that the N-terminal portion of DnaJ, which is conserved in all family members, is essential for this activation reaction. The activated form of DnaK binds preferentially to sigma(32) versus the bacteriophage lambda P protein substrate.