Nucleoskeltal proteins with bifunctional roles in the nucleus and mitotic apparatus: a paradigm for protein dynamics in the cell cycle

Abstract

The eukaryotic cell nucleus, once believed to contain structureless nucleoplasm surrounding chromatin and the nucleolus is now thought to contain an extensive nucleoskeletal matrix on which chromatin, RNP and a complex array of transcription factors, hormone receptors and other regulatory factors are spatially arranged. A distinct nucleoskeleton has been difficult to identify in the intact nucleus, due in part to masking by a dense array of chromatin fibers. However, if chromatin is extracted by nuclease digestion and high salt, an underlying anastomosing network of 9-13 nm core filaments can be demonstrated. The nucleoskeleton resembles the cytoplasmic intermediate filament complex but is confined entirely within the nucleus where it connects the nuclear lamina with various nuclear organelles, forming an integral lattice of fibers collectively called the nuclear matrix. Although the molecular composition of the nucleoskeleton remains elusive, its integrity apparently requires RNP and a growing list of nuclear matrix proteins.Although relatively insoluble within the nuclear compartment, the entire nucleoskeletal framework and associated chromatin is efficiently dismantled, packaged, partitioned and reassembled into daughter nuclei during mitosis.