[IIa/IIo conversion of RNA polymerase II during heat shock]

Heat-shock treatment of cells activates a protein kinase which phosphorylates a heptapeptide analogous to the repeated motif of the C-terminal domain (CTD) of the large subunit of RNA polymerase II from mammalian cells. This is corroborated with a modification of the large subunit of this enzyme during thermal stress in HeLa cells. We have observed a shift from the IIa form (unphosphorylated) to the IIo form (phosphorylated) with a higher apparent molecular weight, during a heat-shock at 44, 45 or 46 degrees C and by a chemical stress induced by sodium arsenite. RNA polymerase II hyperphosphorylation, together with the activation of the heat-shock transcription factor, might contribute to the onset of the preferential transcription of heat-shock genes.