Regulation of the heat shock response in Escherichia coli

Abstract

All organisms utilize the heat shock response to sense the level of unfolded proteins in the cell and adjust the level of chaperones and proteases accordingly. The regulation of the heat shock response has been extensively studied, yet there are still unexplained components. I report three contributions to our understanding of this regulation. First, I show that instead of a single chaperone, a chaperone network consisting of at least DnaK/J and GroEL/S is used to sense unfolded proteins. Second, I provide evidence for an unexpected link between activity control and regulated degradation of cr32 and suggest that an additional, unidentified factor contributes to the regulation o f cr32 activity. These results are based on analysis of a 32 mutants defective in activity regulation. Third, I demonstrate that Hfq, and potentially small RNA binding partners, contribute to regulation of a 32 in at least two distinct ways. Hfq represses DnaK translation, which in turn leads to an increase in a 32 activity. Also, Hfq participates in a process that we have termed “long-term adaptation”, whereby the activity of o32 recovers to normal levels following long-term chaperone overexpression.