Granules 25-30 nm in diameter: basic constituent of the nuclear matrix, chromosome scaffold, and nuclear envelope

Rat liver nuclear matrix and similar structures derived from isolated Chironomus polytene chromosomes, nuclear envelopes, and intranuclear bodies of frog late oocytes (the karyospheres) were studied by electron microscopy with platinum shadowing and negative staining. We have shown that the treatment of whole nuclei, nuclear envelopes, polytene chromosomes, or karyospheres with nonionic detergent, high salt, and RNase and DNase followed by dilute alkali or hyaluronidase digestion reveals numerous rather uniform granules 25-30 nm in diameter. With omission of the nucleases the granules appear to be associated with DNA strands mostly organized in loops. Many granules form clusters and are arranged in linear or arch-like aggregates or cycles resembling the pore complexes. We suppose that these spherical bodies constitute a basic component of the nuclear matrix, chromosome scaffold, and nuclear envelope and are bound together by hyaluronic acid or some similar glycosaminoglycan.