Nuclear matrix proteins are carried within peripheral material of mitotic chromosomes

Immunofluorescent analysis has shown that autoimmune sera M-222 and M-260 are bound to interphase nuclei and mitotic chromosomes of the pig embryo kidney cell culture. The fluorescent stain is diffuse in nuclei and forms a thin fluorescent area around each nucleolus, whereas the nucleolar cores are unstained. The periphery of each mitotic chromosome is stained distinctly. After removal of histones and DNA by the cell treatment with 2 M NaCl and DNase I, the Hoechst 33258 staining of nuclei and chromosomes disappears completely, whereas the pattern of staining with antibodies is not changed as compared with normal cells. Electron microscopy revealed in interphase nuclei after such treatment only lamina, residual nucleoli, and the intranuclear matrix network, and antibodies are bound just to these elements. Molecular mass of proteins bound to these antibodies was determined by immunoblotting. Serum M-260 contained antibodies to a single 65 kDa polypeptide, whereas antibodies to two polypeptides of 47 and 65 kDa were found in M-222. After chromatin removal and revealing nuclear protein matrix, M-222 binds only to 65 kDa polypeptides. Thus, peripheral chromosomal material is involved in transfer of the nuclear matrix polypeptide to daughter nuclei during mitosis.