Evidence for an active role of the DnaK chaperone system in the degradation of σ32

Under non-stressed conditions in Escherichia coli, the heat shock transcription factor sigma(32) is rapidly degraded by the AAA protease FtsH, The DnaK chaperone system is also required for the rapid turnover of sigma(32) in the cell. It has been hypothesized that the DnaK chaperone system facilitates the degradation of sigma(32) by sequestering it from RNA polymerase core. This hypothesis predicts that mutant sigma(32) proteins, which are deficient in binding to RNA polymerase core, will be degraded independently of the DnaK chaperone system. We examined the in vivo stability of such mutant sigma(32) proteins. Results indicated that the mutant sigma(32) proteins as similar as authentic a32 mere stabilized in Delta dnaK and Delta dnaJ/Delta cbpA cells. The interaction between sigma(32) and DnaK/DnaJ/GrpE was not affected by these mutations, These results strongly suggest that the degradation of sigma(32) requires an unidentified active role of the DnaK chaperone system, (C) 2000 Federation of European Biochemical Societies, Published by Elsevier Science B.V. All rights reserved.