The DnaK chaperone modulates the heat shock response of Escherichia coli by binding to the sigma 32 transcription factor.

Abstract

The heat shock response and the heat shock proteins have been conserved across evolution. In Escherichia coi, the heat shock response is positively regulated by the or32 transcriptional factor and negatively regulated by a subset of the heat shock proteins themselves. In an effort to understand the regulation of the heat shock response, we have purified the a 32 polypeptide to homogeneity. During the purification procedure, we found that a large fraction of the overexpressed a32 polypeptide copurifled with the universally conserved DoaK heat shock protein (the prokaryotic equivalent of the 70-kDa heat shock protein, HSP70). Further experiments established that purified a32 bound to DnaK and that this complex was disrupted in the presence of ATP. Consistent with the fact that dnaK756 mutant bacteria overexpress heat shock proteins at all temperatures, purified DnaK756 mutant protein did not appreciably bind to C32

Proteolysis of the phage λ CII regulatory protein by FtsH (HflB) of Escherichia coli

“…The major host chaperones are not required for the proteolysis of CII and the stabilization of CII by CIII Proteolysis of 32 in vivo requires the presence of the DnaK-DnaJ-GrpE chaperone machine (Tilly et al, 1989;Straus et al, 1990;Liberek et al, 1992). In order to test whether host chaperones participate in CII proteolysis and in CIII activity, experiments were performed in isogenic strains carrying mutations affecting different heat-shock ᮊ 1997 Blackwell Science Ltd, Molecular Microbiology, 24, 1303-1310 …”

The DNA-binding activity of the human heat shock transcription factor is regulated in vivo by hsp70.

“…Transcriptional activation of bacterial heat shock genes is regulated by the abundance of an alternate a factor, o2 (17,52). DnaK, the E. coli homolog of hsp70, together with DnaJ and GrpE, physically interacts with c2 (15, 28) and modulates its synthesis and stability (54,56). Negative regulation in S. cerevisiae involves HSF, since the overexpression of heat shock genes that occurs in yeast cells harboring hsp7O mutations can be abolished by mutating the HSE (7).…”

Analysis of σ 32 mutants defective in chaperone-mediated feedback control reveals unexpected complexity of the heat shock response

“…The DnaK/J/GrpE and GroEL/S chaperone machines each constitute a negative feedback loop that couples 32 activity to cellular protein folding state: overexpression of either chaperone machine decreases 32 activity; conversely, chaperone depletion or overexpression of chaperone substrates increases 32 activity (13)(14)(15)(16). The chaperones are likely to act directly on 32 because they bind to 32 and inhibit its activity in a purified in vitro transcription system (17)(18)(19). Regulated degradation of 32 is mediated by the FtsH protease and facilitated by DnaK/J/GrpE and GroEL/S in vivo, but this process has not been completely recapitulated in vitro, where degradation of 32 by FtsH is slow and not facilitated by chaperones (20,21).…”