Hsf1 and Hsp70 constitute a two-component feedback loop that regulates the yeast heat shock response

Area of Science:

• Molecular Biology
• Cellular Stress Response
• Systems Biology

Background:

• Eukaryotic heat shock response models typically involve a negative feedback loop between Hsf1 and molecular chaperones.
• Previous work identified Hsp70 as the repressor of Hsf1 and developed a mathematical model for yeast heat shock response.

Purpose of the Study:

• To validate the assumptions of a mathematical model for the heat shock response.
• To elucidate the quantitative control mechanisms of Hsf1 regulation by Hsp70.

Main Methods:

• Experimental uncoupling of Hsp70 expression from Hsf1 regulation.
• Mapping of Hsp70 binding sites on Hsf1 using in vitro and in vivo assays.
• Analysis of Hsf1 activity in cells with modified conserved element 2 (CE2) and N-terminal domains.

Main Results:

• Hsf1 failed to deactivate efficiently without Hsp70 induction, confirming model predictions.
• A low-affinity Hsp70 binding site was identified in Hsf1's CE2 domain.
• CE2 domain modifications altered Hsf1 deactivation kinetics; N-terminal domain negatively regulates DNA binding.

Conclusions:

• The study validates critical assumptions of the Hsf1-Hsp70 feedback loop model.
• Quantitative insights into Hsf1 regulation by Hsp70 were uncovered.
• The findings reveal precise molecular mechanisms governing the eukaryotic heat shock response.