NONNATIVE PROTEINS INDUCE EXPRESSION OF THE BACILLUS-SUBTILIS CIRCE REGULON

The chaperone-encoding groESL and dnaK operons constitute the CIRCE re gulon of Bacillus subtilis, Both operons are under negative control of the repressor protein HrcA, which interacts with the CIRCE operator a nd whose activity is modulated by the GroESL chaperone machine. In thi s report, we demonstrate that induction of the CIRCE regulon can also be accomplished by ethanol stress and puromycin, Introduction of the h rc4 gene and a transcriptional fusion under the control of the CIRCE o perator into Escherichia coli allowed induction of this fusion by heat shock, ethanol stress, and overproduction of GroESL substrates, The e xpression level of this hrcA-bgaB fusion inversely correlated with the amount of GroE machinery present in the cells. Therefore, all inducin g conditions seem to lead to induction via titration of the GroE chape ronins by the increased level of nonnative proteins formed. Puromycin treatment failed to induce the sigma(B)-dependent general stress regul on, indicating that nonnative proteins in general do not trigger this response. Reconstitution of HrcA-dependent heat shock regulation of B. subtilis in E. coli and complementation of E. coli groESL mutants by B. subtilis groESL indicate that the GroE chaperonin systems of the tw o bacterial species are functionally exchangeable.