Binding of lamin A to polynucleosomes

Morphological observations suggest a close association between heterochromatin and the nuclear lamina. To investigate the molecular aspects of this association, we have established a simple sedimentation assay employing purified lamin proteins, or their 125I-labeled derivatives, and polynucleosomal particles isolated from avian erythrocytes. We report here that purified, unlabeled lamin A and 125I-lamin A, but not 125I-lamin B or 125I-bovine serum albumin, bind to polynucleosomes in a saturable and specific fashion. The specific binding of 125I-lamin A is of high affinity (Kd = approximately 1 x 10(-9) M) and is distinctly temperature-dependent. This interaction is not affected by exogenous polyionic agents such as polylysine and DNA, but it can be abolished by protease digestion of the polynucleosomes. These data suggest that nuclear lamin A maintains a direct association with a proteinaceous constituent of interphase chromatin.