title: [Planar model of nucleosome and chromatin structure of high orders].
abstract: A model of nucleosome is discussed, which consists of two nucleohistone strand folds, located at the same level, similarly directed and having a rhomboid form. The folds are symmetric to each other. Four histones (H3, H2a, H2b and H4) take part in the formation of each fold. Nucleosome begins with a DNA region, bound with H1 histone and terminates with free DNA. Total sequence of histones along DNA is H1-H3-H2a-H2b-H4-H4-H2b-H2a-H3. Polypeptide chains of neighboring histones are oppositely directed and are located at opposite DNA strands. The model explains regularities of chromatin splitting under combined effect of ds-nucleases and trypsin, and of ss-nucleases. It is also in a good agreement with other properties of chromatin. Nucleosomes join to each other "side-to-side" under coincidence of terminal elements with faces of the rhomboid nucleosome structures. The model permits to explain the formation of a highest order structure--a helix of six nucleosomes, forming a fibril of 250--300 A in diameter. The degree of DNA compactness in it reaches 80--100.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002843:Chromatin; D004247:DNA; D003851:Deoxyribonucleases; D006657:Histones; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010446:Peptide Fragments; D011487:Protein Conformation; D014357:Trypsin
chemical_list: D002843:Chromatin; D006657:Histones; D010446:Peptide Fragments; D004247:DNA; D003851:Deoxyribonucleases; D014357:Trypsin
vernacular_title: Proskostnaia model' i struktury khromatina bysshikh poriadkov.