The Integrity of Nuclear Proteins Following Incubation of Isolated Nuclei in vitro

1 Nuclear proteins have been prepared from isolated nuclei of various rat and mouse tissues. The effect on these proteins of incubation of nuclei at 37° C, storage at –40° C and Triton washing is described. 2 Examination by one-dimensional dodecylsulphate-polyacrylamide gel electrophoresis indicated that incubation at 37° C brought about degradation of the Tris-saline-soluble proteins of nuclei prepared from rat liver, spleen and kidney. 3 Two-dimensional electrophoresis, combining isoelectric focusing and dodecylsulphate electrophoresis, indicated a similar effect on the Tris-saline-soluble nuclear proteins of mouse liver; degradation affected all protein species. 4 Examination of histones and non-histone chromatin proteins from mouse liver by two-dimensional electrophoresis showed these protein groups to be stable during incubation of isolated nuclei at 37°C. 5 Storage of rat liver nuclei at –40° C and omission of routine Triton washing during preparation of nuclei were found to have little effect on the Tris-saline-soluble proteins, all degradation being a consequence of the subsequent incubation at 37°C. 6 Degradation of this same group of proteins did not occur during incubation of isolated nuclei from a rat ascites tumour or regenerating rat liver, 16 h after partial hepatectomy.