TEM image of frozen hydrated soluble chromatin isolated from chicken erythrocyte nuclei and vitrified in low salt. Polynucleosomes adopt an irregular zigzag fiber conformation (a,b,k), and show a 'stem' motif. Similar features are seen in reconstituted polynucleosomes (c,d,f-i). However, if reconstitutes lack linker histone H5, the stem conformation is absent (c). See Fig 1 in J Bednar et al. 1998 Nucleosomes, linker DNA and linker histone form a unique structural motif that directs the higher-order folding and compaction of chromatin. Proc Natl Acad Sci USA 95:14173-14178.
Isolated nuclei were prepared from chicken erythrocyte nuclei and polynucleosomes released after treatment with micrococcal nuclease. Reconstituted polynucleosomes were prepared by salt dialysis using purified DNA and histones. Samples were fixed with 0.1% glutaraldehyde for 4 hr at 4C, placed on holey carbon films, vitrified by plunge freezing, and observed in the frozen hydrated state using a Philips CM10 TEM operated at 60KV. Low dose images were recorded on Kodak SO163 film. See also: J Bednar et al. 1998 Nucleosomes, linker DNA and linker histone form a un ique structural motif that directs the higher-order folding and compaction of chromatin. Proc Natl Acad Sci USA 95:14173-14178.
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