Nuclear substructure antigens. Monoclonal antibodies against components of nuclear matrix preparations.

We describe two monoclonal antibodies, I-2 and I-14, which recognize, respectively, proteins of 36 and 40 kD. By immunofluorescence microscopy on chick embryo fibroblasts, both antigens were found to be located within a nuclear substructure which excludes nucleoli and part of the nucleoplasm; hence we refer to these antigens as nuclear substructure antigens. By immuno-electron microscopy on chick liver sections, the I-14 antigen was identified predominantly in clusters of interchromatin granules and in perichromatin fibrils. The two substructure antigens share a remarkable resistance to sequential extraction of nuclei with DNase I, RNase A, non-ionic detergent and high salt, indicating that they constitute part of an operationally defined residual nuclear matrix. Finally, both substructure antigens are virtually absent from the nuclei of adult erythrocytes. These properties suggest that substructure antigens may be involved in RNA transcription, processing or transport, possibly by contributing nucleoskeletal support.