title: Both ambient temperature and the DnaK chaperone machine modulate the heat shock response in Escherichia coli by regulating the switch between sigma 70 and sigma 32 factors assembled with RNA polymerase.
abstract: In Escherichia coli individual sigma factors direct RNA polymerase (RNAP) to specific promoters. Upon heat shock induction there is a transient increase in the rate of transcription of approximately 20 heat shock genes, whose promoters are recognized by the RNAP-sigma 32 rather than the RNAP-sigma 70 holoenzyme. At least three heat shock proteins, DnaK, DnaJ and GrpE, are involved in negative modulation of the sigma 32-dependent heat shock response. Here we show, using purified enzymes, that upon heat treatment of RNAP holoenzyme the sigma 70 factor is preferentially inactivated, whereas the resulting heat-treated RNAP core is still able to initiate transcription once supplemented with sigma 32 (or fresh sigma 70). Heat-aggregated sigma 70 becomes a target for the joint action of DnaK, DnaJ and GrpE proteins, which reactivate it in an ATP-dependent reaction. The RNAP-sigma 32 holoenzyme is relatively stable at temperatures at which the RNAP-sigma 70 holoenzyme is inactivated. Furthermore, we show that formation of the RNAP-sigma 32 holoenzyme is favored over that of RNAP-sigma 70 at elevated temperatures. We propose a model of negative autoregulation of the heat shock response in which cooperative action of DnaK, DnaJ and GrpE heat shock proteins switches transcription back to constitutively expressed genes through the simultaneous reactivation of heat-aggregated sigma 70, as well as sequestration of sigma 32 away from RNAP.
authors.affiliation: Department of Molecular Biology, University of Gdansk, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Blaszczak
authors.forename: M
authors.initials: M
authors.lastname: Zylicz
authors.forename: C
authors.initials: C
authors.lastname: Georgopoulos
authors.forename: K
authors.initials: K
authors.lastname: Liberek
mesh_terms: D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D018869:Heat-Shock Response; D006358:Hot Temperature; D008957:Models, Genetic; D018832:Molecular Chaperones / Q000378:metabolism; D011485:Protein Binding; D012808:Sigma Factor / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; C081775:RNA polymerase sigma 70; D012321:DNA-Directed RNA Polymerases; C063842:dnaK protein, E coli