A CYCLE OF BINDING AND RELEASE OF THE DNAK, DNAJ AND GRPE CHAPERONES REGULATES ACTIVITY OF THE ESCHERICHIA-COLI HEAT-SHOCK TRANSCRIPTION FACTOR SIGMA(32)

The chaperone system formed by DnaK, DnaJ and GrpE mediates stress-dep endent negative modulation of the Escherichia coli heat shock response , probably through association with the heat shock promoter-specific s igma(32) subunit of RNA polymerase. Interactions of the DnaK system wi th sigma(32) were analysed. DnaJ and DnaK bind free, but not RNA polym erase-bound, sigma(32) with dissociation constants of 20 nM and 5 mu M respectively. Association and dissociation rates of DnaJ-sigma(32) co mplexes are 5900- and 20-fold higher respectively than those of DnaK-s igma(32) complexes in the absence of ATP. ATP destabilizes DnaK-sigma( 32) interactions. DnaJ, through rapid association with sigma(32) and s timulation of hydrolysis of DnaK-bound ATP, mediates efficient binding of DnaK to sigma(32) in the presence of ATP, resulting in DnaK-DnaJ-s igma(32) complexes containing ADP. GrpE binding to these complexes sti mulates nucleotide release and subsequent complex dissociation by ATP. We propose that the principles of this cycle also operate in other ch aperone activities of the DnaK system. DnaK and DnaJ cooperatively inh ibit sigma(32) activity in heat shock gene transcription and GrpE part ially reverses this inhibition. These data indicate that reversible in hibition of sigma(32) activity through transient association of DnaK a nd DnaJ is a central regulatory element of the heat shock response.