Core filaments of the nuclear matrix.
The nuclear matrix is concealed by a much larger mass of chromatin, which can be removed selectively by digesting nuclei with DNase I followed by elution of chromatin with 0.25 M ammonium sulfate. This mild procedure removes chromatin almost completely and preserves nuclear matrix morphology. The complete nuclear matrix consists of a nuclear lamina with an interior matrix composed of thick, polymorphic fibers and large masses that resemble remnant nucleoli. Further extraction of the nuclear matrices of HeLa or MCF-7 cells with 2 M sodium chloride uncovered a network of core filaments. A few dark masses remained enmeshed in the filament network and may be remnants of the nuclear matrix thick fibers and nucleoli. The highly branched core filaments had diameters of 9 and 13 nm measured relative to the intermediate filaments. They may serve as the core structure around which the matrix is constructed. The core filaments retained 70% of nuclear RNA. This RNA consisted both of ribosomal RNA precursors and of very high molecular weight hnRNA with a modal size of 20 kb. Treatment with RNase A removed the core filaments. When 2 M sodium chloride was used directly to remove chromatin after DNase I digestion without a preceding 0.25 M ammonium sulfate extraction, the core filaments were not revealed. Instead, the nuclear interior was filled with amorphous masses that may cover the filaments. This reflected a requirement for a stepwise increase in ionic strength because gradual addition of sodium chloride to a final concentration of 2 M without an 0.25 M ammonium sulfate extraction uncovered core filaments.
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Department of Biology, Beijing Normal University, Peoples Republic of China.
Nickerson
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JA
Penman
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D002460:Cell Line; D002843:Chromatin / Q000648:ultrastructure*; D004273:DNA, Neoplasm / Q000032:analysis; D006367:HeLa Cells / Q000648:ultrastructure; D006801:Humans; D008854:Microscopy, Electron; D008970:Molecular Weight; D015530:Nuclear Matrix / Q000648:ultrastructure*; D009687:Nuclear Proteins / Q000032:analysis; D012322:RNA Precursors / Q000302:isolation & purification; D012332:RNA, Heterogeneous Nuclear / Q000302:isolation & purification; D012334:RNA, Neoplasm / Q000302:isolation & purification; D012335:RNA, Ribosomal / Q000302:isolation & purification
D002843:Chromatin; D004273:DNA, Neoplasm; D009687:Nuclear Proteins; D012322:RNA Precursors; D012332:RNA, Heterogeneous Nuclear; D012334:RNA, Neoplasm; D012335:RNA, Ribosomal