Revival of the heat shock response after two decades with a small Hsp in a critical but distinct act.

The heat stress response is an essential defense mechanism in all organisms. Heat shock proteins (Hsps) are produced in response to thermal stress, with their expression levels regulated by heat shock transcription factors. In the key transcription factor σ positively regulates Hsp expression. Studies from over two decades ago revealed that σ abundance is negatively controlled under normal conditions, mainly through degradation mechanisms involving DnaK, GroEL, and FtsH. Beyond this established mechanism, recent findings indicate that a small heat shock protein IbpA also plays a role in the translational regulation of σ, adding a new layer to the established model. This review highlights the role of a new actor, IbpA, which strongly suppresses σ expression under non-stress conditions and markedly increases it during heat shock.