NUCLEAR-MITOTIC APPARATUS PROTEIN - A STRUCTURAL PROTEIN INTERFACE BETWEEN THE NUCLEOSKELETON AND RNA SPLICING

Vertebrate splicing factors are localized to discrete domains within t he nuclei of somatic cells. The mechanism whereby such nuclear domains , identified as speckles by immunofluorescence microscopy, are generat ed is unclear. Recent studies suggest that the spatial order within th e nucleus is maintained by nuclear matrix factors. Here we show that a protein in the nuclear matrix and mitotic apparatus [nuclear-mitotic apparatus protein, NuMA; Lydersen, B. & Pettijohn, D. (1980) Cell 22, 489-499] colocalizes with splicing factors in interphase nuclei and is associated with small nuclear ribonucleoproteins in a complex immunop recipitated from HeLa extract with small nuclear ribonucleoprotein ant ibodies. Moreover, NuMA associates with splicing complexes that are re constituted in vitro using wild-type pre-mRNA, but not with nonspecifi c RNA. Cumulatively, these observations suggest a function of NuMA or NuMA-like proteins in interphase cells in providing a bridge between R NA processing and the nucleoskeleton.