The Escherichia coli small heat shock protein IbpA plays a role in regulating the heat shock response by controlling the translation of σ32

Small heat shock proteins (sHsps) act as ATP-independent chaperones that prevent irreversible aggregate formation by sequestering denatured proteins. IbpA, an Escherichia coli sHsp, functions not only as a chaperone but also as a suppressor of its own expression through posttranscriptional regulation, contributing to negative feedback regulation. IbpA also regulates the expression of its paralog, IbpB, in a similar manner, but the extent to which IbpA regulates other protein expressions is unclear. We have discovered that IbpA downregulates the expression of many Hsps by repressing the translation of the heat shock transcription factor {sigma}32. The IbpA regulation not only controls the {sigma}32 level but also contributes to the shut-off of the heat shock response. These results revealed an unexplored role of IbpA to regulate heat shock response at a translational level, which adds a new layer for tightly controlled and rapid expression of {sigma}32 on demand. Significance StatementTo survive during heat shock, cells have a mechanism to induce the synthesis of Hsps and to restore normal levels when the stress subsides. The molecular mechanisms of the heat shock response in E. coli have been extensively studied over the years. The master heat shock transcriptional regulator, {sigma}32, which is normally at low levels due to chaperone-mediated degradation, is increased upon heat shock. Our study has identified a previously unknown factor, IbpA, that regulates the level of {sigma}32 by suppressing its expression at a translational level, thereby contributing to the heat shock response regulation.