DnaK, DnaJ, and GrpE heat shock proteins negatively regulate heat shock gene expression by controlling the synthesis and stability of σ32

Abstract

The Escherichia coli DnaK heat shock protein has been identified previously as a negative regulator of E. coli heat shock gene expression. We report that two other heat shock proteins, DnaJ and GrpE, are also involved in the negative regulation of heat shock gene expression. Strains carrying defective dnaK, dnaJ, or grpE alleles have enhanced synthesis of heat shock proteins at low temperature and fail to shut off the heat shock response after shift to high temperature. These regulatory defects are due to the loss of normal control over the synthesis and stability of σ32, the alternate RNA polymerase σ-factor required for heat shock gene expression. We conclude that DnaK, DnaJ, and GrpE regulate the concentration of σ32. We suggest that the synthesis of heat shock proteins is controlled by a homeostatic mechanism linking the function of heat shock proteins to the concentration of σ32.