On the existence of an internal nuclear protein structure in HeLa cells

Abstract

When nuclei of HeLa cells are depleted of membranes, soluble molecules, RNA, DNA and their associated proteins by subsequent treatments with detergents, nucleases and a high-salt buffer, a structure remains that consists of residual nucleoli, internal fibrogranular structures and remnants of the peripheral pore-complex lamina. This proteinaceous structure, referred to as nuclear matrix, which is essentially free of nucleic acids, is apparently not formed by artificial disulphide bridges, since preventing disulphide bridge formation during cell fractionation by addition of iodoacetamide or 2-mercaptoethanol does not affect the morphology and composition of the isolated matrices. It is shown that specific proteins of the matrix interact with antibodies from sera of patients suffering from an autoimmune disorder. When purified IgG fractions of these sera are used for immunofluorescence studies on whole HeLa cells, isolated nuclei or nuclear matrices the same type of fluorescent pattern, a speckled nuclear fluorescence (the cytoplasm and nucleoli being negative) is obtained. These results support the concept that an internal proteinaceous network is part of the isolated nuclear matrix and that this intranuclear structure represents a framework that exists in vivo.