Nuclear skeleton structures in some normal and tumor cells.

Nuclear protein fractions, described earlier, were identified as constituents of the nuclear sap (the 'globulin fraction'), that of the nucleoli and ribonucleoprotein network (the 'acidic protein'), and of the nuclear envelope (the 'residual protein'). The latter two fractions compose the protein skeleton of the cell nucleus. An essential difference between electrophoretic profiles of nuclear skeleton structures in experimental tumors and those of normal tissues was revealed. Tumor preparations contained more high molecular weight polypeptides and, in earlier stages of growth, low molecular weight components as well. Fractionation of the nuclear matrix proteins showed that the bulk of them are soluble in diluted alkali. The alkali-insoluble fraction retains the shape of the nucleus and appears in the electron microscope as a spongy nuclear skeleton. A finely dispersed fraction sedimenting from the alkaline suspension is enriched with the pore complexes. The fractions obtained differ in protein composition and probably contain protein components which are similar in molecular weights but non-identical.