Monoclonal antibodies specific for tight-binding human chromatin antigens reveal structural rearrangements within the nucleus during the cell cycle.

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Abstract
The class of nonhistone chromosomal proteins that remains bound to DNA in chromatin in the presence of 2.5 M NaCl-5 M urea has proven refractile to biochemical analysis. In order to study its role in chromatin organization, monoclonal antibodies were produced that are specific for the HeLa DNA-protein complex that remains after extraction of chromatin with high salt and urea. The antibody-producing clones were identified with an ELISA [enzyme-linked immunosorbent assay] assay. Of the 6 clones selected, 5 were stabilized by limiting dilution. All clones are IgG producers None cross-react significantly with native DNA, core histones, or the high-mobility group nonhistone proteins. All antibodies are specific for nuclear or juxtanuclear antigens. Indirect immunofluorescence shows that 3 antibodies, which are nonidentical, stain 3 different nuclear networks. Available evidence indicates that 2 of these networks are the nuclear matrix. A 4th antibody reveals structures reminiscent of chromocenters. A 5th antibody, AhNA-1, binds to interphase HeLa chromatin and specifically decorates metaphase chromosomes. AhNA-1 similarly recognizes rat chromosomes. Each of these monoclonal antibodies also reveals a changing pattern of nuclear staining as cells progress through the cell cycle. Presumably, this reflects the rearrangement of the cognate antigens.