Localization of the heat shock-induced proteins in Drosophila melanogaster tissue culture cells

The exposure of Drosophila melanogaster tissue culture cells to 37°C induces the synthesis of a new set of proteins, the heat shock proteins, while the synthesis of most of the proteins actively made before the heat shock is strongly repressed. Cellular localization of the heat shock proteins has been studied in different cell fractions and by electron microscope autoradiography of cell sections. The results indicate that the heat shock proteins of 22, 23, 26, and 27 kdaltons and at least a fraction of the 68- and 70-kdalton proteins are found in the nucleus after the heat shock, where they are present in chromatin and nucleoli preparations. When the temperature is shifted back to 25°C, the synthesis of the heat shock proteins regresses and stops after several hours, while the proteins normally synthesized at 25°C reappear. At 25°C, a large proportion of the heat shock proteins leaves the nucleus and is predominantly localized in the cytoplasm.