Evidence for an active role of the DnaK chaperone system in the degradation of sigma(32).
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 sigma(32) were stabilized in DeltadnaK and DeltadnaJ/DeltacbpA 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.
Division of Molecular Cell Biology, Institute of Molecular Embryology and Genetics, Kumamoto University, Japan.
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Akiyama
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Ogura
D049069:ATP-Dependent Proteases; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; C085674:CbpA protein, E coli; D004268:DNA-Binding Proteins; C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; C068113:GrpE protein, Bacteria; C489400:GrpE protein, E coli; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; D012321:DNA-Directed RNA Polymerases; D049069:ATP-Dependent Proteases; C513383:FtsH protein, E coli; C063842:dnaK protein, E coli