Cross-reaction of hnRNP-proteins of HeLa cells with nuclear proteins of Drosophila melanogaster demonstrated by a monoclonal antibody

A monoclonal antibody from clone T7 raised against total nuclear proteins from the Kc cell line of Drosophila melanogaster (Saumweber, H. Symmons. P. Kabisch, R. Will, HBonhoeffer, F, Chromosoma 80 (1980) 253) [1] showed positive immunofluorescent staining on interphase nuclei of HeLa and PTK2 cells. When this antibody was allowed to react with several nuclear protein fractions isolated from HeLa S3 cells, three polypeptides of molecular weights (MW) 44 000, 63 000 and 70 000 were identified as the corresponding antigens, all components of hnRNA containing ribonucleoprotein particles. Sucrose gradient fractionation of such particles after mild RNase treatment and subsequent analysis of the proteins by the immunoblotting method revealed that the 44 000 MW antigen was an integral part of the ribonuclease-resistant complex. The results support the view that hnRNA molecules are associated with certain proteins conserved during evolution which may play structural roles in the ribonucleoprotein organization.