Heat‐shock and related stress enhance RNA polymerase II C‐terminal‐domain kinase activity in HeLa cell extracts

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Abstract
Changes in protein kinase activities are thought to contribute to the alteration of gene expression after heat shock and related stresses. In an attempt to identify enzymes which might be involved in both chromatin structure modification and transcriptional switch in heat‐shocked cells, we have studied protein kinase activities in heat‐shocked cell lysates with two exogenous substrates: a tetramer of a heptapeptide (heptapeptide 4) corresponding to the RNA polymerase II C‐terminal domain (CTD), and the histone H1. Heat‐shock and arsenite stress were found to stimulate strongly CTD kinase activity. H1 kinase activity was also stimulated but more weakly. Stimulation of CTD and H1 kinases occurs mainly at the early phase of recovery and by a process which is independent of protein synthesis. The stress‐induced H1 kinase is shown to contain a molecule related to the mitotic‐promoting factor (MPF) Cdc2 component. On the other hand, though Cdc2‐related protein has also been reported to be part of a CTD kinase complex, we show that the stress‐induced CTD kinase activity corresponds to a distinct entity. It is proposed that stress activation of CTD kinase might be involved in changing the specificity of RNA polymerase II.