THE GROE CHAPERONIN MACHINE IS A MAJOR MODULATOR OF THE CIRCE HEAT-SHOCK REGULON OF BACILLUS-SUBTILIS

Class I heat-inducible genes in Bacillus subtilis consist of the hepta cistronic dnaK and the bicistronic groE operon and form the CIRCE regu lon, Both operons are negatively regulated at the level of transcripti on by the HrcA repressor interacting with its operator, the CIRCE elem ent, Here, we demonstrate that the DnaK chaperone machine is not invol ved in the regulation of HrcA and that the GroE chaperonin exerts a ne gative effect in the post-transcriptional control of HrcA, When expres sion of the groE operon was turned off, the dnaK operon was significan tly activated and large amounts of apparently inactive HrcA repressor were produced, Overproduction of GroEL, on the other hand, resulted in decreased expression of the dnaK operon, Introduction of the hrcA gen e and its operator into Escherichia coli was sufficient to elicit a tr ansient heat shock response, indicating that no additional Bacillus-sp ecific gene(s) was needed, As in B. subtilis, the groEL gene of E. col i negatively influenced the activity of HrcA. HrcA could be overproduc ed in E. coli, but formed inclusion bodies which could be dissolved in 8 M urea, Upon removal of urea, HrcA had a strong tendency to aggrega te, but aggregation could be suppressed significantly by the addition of GroEL. Purified HrcA repressor was able specifically to retard a DN A fragment containing the CIRCE element, and the amount of retarded DN A was increased significantly in the presence of GroEL, These results suggest that the GroE chaperonin machine modulates the activity of the HrcA repressor and therefore point to a novel function of GroE as a m odulator of the heat shock response.