Comparison of the proteins present in HeLa cell interphase nucleoskeletons and metaphase chromosome scaffolds.

The nucleoskeleton, a macromolecular complex whose major structural elements are DNA and protein, is purported to be at least in part responsible for the gross morphology of the nucleus. This structure can be isolated from the nuclei of cells in all stages of the cell cycle with the exception of mitosis when no nuclei are present. We had previously proposed that during mitosis, the nucleoskeletal elements are reorganized and become part of mitotic chromosomes (Keller, J. M., and Riley, D. E. (1976) Science 193, 399-401). In order to test this possibility, we have compared the proteins of the nucleoskeleton to chromosomal proteins of similar solubility by one- and two-dimensional polyacrylamide gel electrophoresis and by peptide mapping. We have found that the major proteins of the nucleoskeleton are also major proteins of the chromosome scaffold. In addition, our data indicate that at least two of the nucleoskeletal proteins may be modified during the transition of the cell into mitosis. These data suggest that the nuclear dissolution associated with open mitosis is accompanied by a gross rearrangement of the nucleoskeletal elements to form components of metaphase chromosomes. This reorganization may be triggered by modification of several of the nucleoskeletal proteins. These observations appear to distinguish the nucleoskeletal proteins from the major nuclear lamina proteins which have been shown by others to be dispersed throughout the cell at mitosis.