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

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.