Phosphorylation-mediated regulation of heat shock response in Escherichia coli

Escherichia coli has two heat shock regulons under the transcriptional control of Esigma32 and EsigmaE RNA polymerases. These polymerases control the expression of genes, the products of which are needed for correct folding of proteins in the cytoplasm and the extracytoplasm respectively. In this study, we report that mutations in a tyrosine phosphatase-encoding gene led to decreased activity of these heat shock regulons. The activity of the tyrosine phosphatase is presumably co-ordinated with that of a cognate kinase. We show here that mutants deleted for the phosphatase-encoding gene accumulate phosphorylated RpoH. We find that RpoH is phosphorylated at amino acid position 260, which is located in the conserved region 4.2, and that this phosphorylation event attenuates RpoH activity as a sigma factor. The rpoH Tyr-260Ala mutation confers a temperature-sensitive phenotype that leads to an altered heat shock response. Additionally, we show that the antisigma factor RseA is phosphorylated at the N-terminally located Tyr-38 and that this phosphorylation presumably alters its binding affinity towards sigmaE.