Effect of divalent cations on the extraction of nuclear proteins

TSCM-(0.01 M Tris-HCl, 0.25 sucrose, 3.8 mM CaCl2, 12 mM MgCl2, pH 7.2) and TS-(0.01 M Tris-HCl, 0.25 M sucrose, pH 7.2)-soluble proteins of isolated rat liver nuclei were analyzed by a two-dimensional polyacrylamide gel electrophoresis method. Light microscopy showed that treatment with the TSCM solution did not alter the morphology of isolated nuclei. After treatment with the divalent cation-free TS solution, the isolated nuclei were swollen; some were disrupted and clumped together. The TSCM solution extracted 20 additional proteins including histones. These results suggest that Ca++ and Mg++ play an intracellular role in the interactions between nuclear proteins and chromatin.