Presence of a novel nuclear lamina protein in Raji cells

In mammalian tissues, the nuclear lamina is composed of the major lamins A, B, and C, and minor lamins D/E. Although lamin B is present in all cell types, lamins A and C are absent from embryonic cells and most undifferentiated cells from hematopoietic lineage. We have investigated the nuclear lamina protein composition of the Raji cell line, lymphoblast-like cells established from a Burkitt lymphoma patient. Lamins A and C were confirmed absent by immunodetection and Northern blot analysis. Besides lamins B and D/E, a protein migrating around 71 kilodaltons was recognized by a serum directed against the nuclear lamina of BHK-21 fibroblasts. Cellular localization by sequential extraction established this 71-kilodalton protein as an exclusive component of the nuclear lamina fraction. These results indicate that the nuclear lamina has a more complex composition than previously thought to be the case for cells devoid of lamins A and C.