A HUMAN AUTOANTIBODY RECOGNIZING NUCLEAR MATRIX-ASSOCIATED NUCLEAR-PROTEIN LOCALIZED IN DOT STRUCTURES

A human autoimmune serum is used to characterize a protein which is lo cated within a dot-like structure of the interphase nucleus. The dots are located in the nucleoplasma outside the nucleoli. The dot-like str ucture could be observed on a variety of human substrates (HEp-2, HepG 2, HeLa, Molt-4, WI-38 cell lines, peripheral blood lymphocytes), mous e cell lines and tissues (3T3, L929, spleen sections), rat sections, m arsupial PtK2 cells and hamster cell lines. The range of the number of dots and their size differed between cells and cell lines and varied between 1 and 24. The antigen could be identified as a 53 kDa protein with a pi of 8.7 and was named NDP53. Digestion experiments suggested that the protein is not associated with DNA or RNA, but is associated with the nuclear matrix. Immunelectron microscopy using ultra-thin sec tions revealed filamentous structures with a diameter of 0.1 to 0.6 mu m. The antigen colocalizes with Sp100, PML and NDP55, which are part of a multiprotein complex known as PML oncogenic domain (POD), nuclear bodies, Kr bodies or ND10.