标题：Subunit structure of chromatin and the organization of eukaryotic highly repetitive DNA: Nucleosomal proteins associated with a highly repetitive mammalian DNA
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1977
卷号：74
期号：8
页码：3297-3301
DOI：10.1073/pnas.74.8.3297
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Component DNA is a homogeneous, highly repetitive fraction that comprises nearly a quarter of the African green monkey (Cercopithecus aethiops) genome. By restriction enzyme analysis, it has a repeat periodicity of 176 {+/-} 4 nucleotide base pairs, corresponding closely with the length of DNA contained within a nucleosome. The sequence is organized into large blocks of constitutive heterochromatin. A method is described here for the isolation of intact polynucleosomal arrays containing only component sequences. Isolated monkey nuclei are treated with EcoRI, which releases only component nucleosomal arrays; the arrays are then fractionated and purified by sedimentation in sucrose gradients. The method permits a compositional analysis of the proteins associated with a constitutively repressed, heterochromatic sequence. The major differences in the proteins associated with component nucleosomes that distinguish them from the bulk DNA nucleosomes are a decrease in the content of the H1 histones in the component nucleosomes and a concomitant increase in the amount of certain nonhistone proteins. The specific observations are: (i) In the component nucleosomes, 65-70% of the proteins were nonhistone proteins; this contrasts with the value, 40%, for nonhistone proteins associated with nucleosomes containing bulk DNA. (ii) The amount of H1 histone in chromatin containing predominantly bulk DNA was about 13.7%. However, the H1 histone was depleted and possibly absent in component oligonucleosomes. (iii) Coincident with the decrease in the H1 histones and in the same molecular weight range (24,000-43,000), there appeared five minor nonhistone proteins. The minor, low-molecular-weight, nonhistone proteins were not detected in chromatin containing bulk DNA but they represented nearly 12% of the protein in component nucleosomes. The resistance to salt extraction (0.6-2.0 M NaCl) indicates that the low-molecular-weight nonhistone proteins are tenaciously bound to the component nucleosomes. In addition, a class of high-molecular-weight (>100,000) nonhistone proteins was enriched 5- or 6-fold in component oligonucleosomes. The relative amounts of the nucleosome core histones were not changed.
关键词：Eco RI restriction endonuclease ; nucleosome fractionation ; mammalian repetitive DNA sequences ; histone and nonhistone proteins
