The Structure of Satellite-Containing Chromatin of the Rat
During the last decade the main principles and general features of the chromatin structure have been established. The basic repetitive unit within the hierarchy of chromatin superstructures is the nucleosome, a structure revealed both by nuclease digestion of chromatin1,3 and by visualization of chromatin in the electron microscope4. At a second level of chromatin organization, the polynucleosomal chain (100 Å filament) is condensed into 250–300 A fibers. Although most of the experimental results suggest that the polynucleosomal chain in these fibers is organized in a continuous helical fashion called a solenoid5, alternative structures with discontinuous globular particles called superbeads6,7 or other arrangements involving four interwoven filaments8 have been proposed. At a third level, the 250–300 Å fibers are folded into loops or domains in both interphase nuclei and metaphase chromosomes9-11. While these three levels of condensation may account for the compaction of chromatin in interphase, additional levels of compaction were suggested in metaphase chromosomes12,13. (For comprehensive reviews on chromatin structure see references 14, 15).
KeywordsRepeat Length Chromatin Fiber Micrococcal Nuclease Nonhistone Protein Satellite Unit
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