Putative function of Drosophila melanogaster heat shock proteins in the nucleoskeleton

The cellular distribution in Drosophila Kc cells of [35S]methionine-labeled heat shock proteins has been examined by 0.2% Nonidet P-40-mediated cell lysis and Na-deoxycholate-Tween 40 extraction of the nuclei. The 83,000-dalton heat shock protein was limited to the detergent extracts while the remaining heat shock proteins were found both in a soluble pool in the detergent extracts and in a bound pool in the nuclei. The bound pool included the 70,000-68,000-, 27,000-, 26,000-, 23,000-, and 21,000-dalton heat shock proteins; these proteins accumulated in the nuclei during the time course of heat shock as assayed by [35S]methionine labeling and dye binding on gel electropherograms. DNA and histone-depleted nuclei were prepared by extensive nuclease digestion, 2.0 M NaCl extraction, and sedimentation of the original detergent-washed nuclei. Of the 35S-labeled bound pool, 69% remained associated in a rapidly sedimenting complex that retained only approximately 5% of the DNA. Thus, the binding of the 70,000-68,000-, 27,000-, 26,000-, 23,000-, and 21,000-dalton heat shock proteins appeared primarily to be with the nuclear scaffold rather than the chromatin. We conclude from the mass of heat shock protein synthesis that these proteins probably are structural elements of the nucleus.