PURIFICATION OF INTACT NUCLEAR LAMINA AND IDENTIFICATION OF NOVEL LAMINLIKE PROTEINS IN RAJI, A CELL-LINE DEVOID OF LAMIN-A AND LAMIN-C

Research on the structure of the: nuclear lamina and the nuclear matri x of cells devoid of lamins A and C has been hampered by the fact that intact residual nuclear structures are difficult to isolate from such cells. In this paper. we show that some extraction parameters, such a s buffer composition and the nature of the detergent used to remove nu clear membranes, are critical for achieving isolation of whole nuclear residual structures from the lymphoblastic cell line Raji, used as a model for cells without lamins A and C. Electron microscopic analysis shows that the nuclear lamina of Raji cells is formed by a network of intermediate-sized filaments interrupted with circular discontinuities . Both lamins B1 and B2, and lamin D/E, are present in this structure. In addition, a group of 45-kDa proteins or intermediate filament prot ein-reacting proteins (IFA-RPs), located uniquely in the lamina: were found to exhibit the same immunological and chemical characteristics a s lamins. Although they behave like nuclear lamins, microsequencing an alysis of the IFA-RPs has revealed no homology with known lamins. Thes e IFA-RPs may contribute to the formation of the nuclear lamina filame nt network in the absence of lamins A and C.