Higher-order structure of long repeat chromatin.
The higher-order structure of chromatin isolated from sea urchin sperm, which has a long nucleosomal DNA repeat length (approximately 240 bp), has been studied by electron microscopy and X-ray diffraction. Electron micrographs show that this chromatin forms 300 A filaments which are indistinguishable from those of chicken erythrocytes (approximately 212 bp repeat); X-ray diffraction patterns from partially oriented samples show that the edge-to-edge packing of nucleosomes in the direction of the 300 A filament axis, and the radial disposition of nucleosomes around it, are both similar to those of the chicken erythrocyte 300 A filament, which is described by the solenoid model. The invariance of the structure with increased linker DNA length is inconsistent with many other models proposed for the 300 A filament and, furthermore, means that the linker DNA must be bent. The low-angle X-ray scattering in the 300-400 A region both in vitro and in vivo differs from that of chicken erythrocyte chromatin. The nature of the difference suggests that 300 A filaments in sea urchin sperm in vivo are packed so tightly together that electron-density contrast between individual filaments is lost; this is consistent with electron micrographs of the chromatin in vitro.
D000818:Animals; D002843:Chromatin / Q000648:ultrastructure*; D004247:DNA / Q000032:analysis; D008297:Male; D008854:Microscopy, Electron; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000648:ultrastructure; D012091:Repetitive Sequences, Nucleic Acid; D012617:Sea Urchins; D013094:Spermatozoa / Q000648:ultrastructure; D014961:X-Ray Diffraction
D002843:Chromatin; D009707:Nucleosomes; D004247:DNA