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

In Escherichia coil the heat shock response is under the positive cont rol of the sigma(32) transcription factor. Three of the heat shock pro teins, DnaK, DnaI, and GrpE, play a central role in the negative autor egulation of this response at the transcriptional level. Recently, we have shown that the DnaK and DnaJ proteins can compete with RNA polyme rase 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. R esults obtained with two DnaJ mutants, a missense and a truncated vers ion, suggest that the N-terminal portion of DnaJ, which is conserved i n all family members, is essential for this activation reaction. The a ctivated form of DnaK binds preferentially to sigma(32) versus the bac teriophage lambda P protein substrate.