Ultrastructural study of chromatin fibrils in thin sections of isolated nuclei.
In ultrathin sections of isolated rat liver nuclei and chromatin fibril represents a chain of 250-A globules. Electron microscopic examination of the physiologically loose globules of diffuse chromatin or globules of compact chromatin loosened by heparin treatment has revealed that each 250-A globule contains a nucleosome covered with 60--85-A thick layer -- "a capsule of a nucleosome". Some filaments, approximately 20 A in diameter, can be distinguished within the capsule each being attached to the nucleosome by a dark granule. Chromatin fibril has an axis representing "beads-on-a-string" -- a chain of nucleosomes interconnected with 25-A thick filaments. Some implications of the capsule molecular composition and of its role in transcription are suggested. A model of 250 A chromatin globule as well as of chromatin fibril, different from either the solenoid model or the superbead one is put forward.
D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure*; D002478:Cells, Cultured; D002843:Chromatin / Q000648:ultrastructure*; D008099:Liver / Q000648:ultrastructure*; D008297:Male; D008854:Microscopy, Electron; D009707:Nucleosomes / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains
D002843:Chromatin; D009707:Nucleosomes