Nucleosome positioning is determined by the (H3-H4)2 tetramer.
It is demonstrated that the histone (H3-H4)2 tetramer can find specific positions on DNA, even in the absence of other histones. Purified histone (H3-H4)2 tetramers were reconstituted onto 208-base-pair (bp) DNA molecules containing a nucleosome-positioning sequence by using salt-gradient dialysis. The stoichiometry of histone tetramer to DNA was shown to be 1:1. Digestion with micrococcal nuclease led to formation of protected DNA fragments of approximately 73 bp. Cleavage of the 73-bp DNA with restriction enzymes produced a small set of defined bands, demonstrating positioning of the (H3-H4)2 tetramer on DNA. Analysis of the restriction digests shows that the 73-bp DNA corresponds mainly to two fragments, one lying on either side of the pseudo-dyad axis of the major position adopted by complete histone octamers on this DNA. This result means that a single (H3-H4)2 histone tetramer can fold approximately 146 bp of DNA with the same positioning as the complete octamer but that a region near the pseudo-dyad is only weakly protected against micrococcal nuclease attack in the absence of histones H2A and H2B.
Dong
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Department of Biochemistry and Biophysics, Oregon State University, Corvallis 97331-6503.
van Holde
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KE
D000818:Animals; D002645:Chickens; D002843:Chromatin / Q000378:metabolism; D004247:DNA / Q000235:genetics / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism; D006657:Histones / Q000302:isolation & purification / Q000378:metabolism*; D046911:Macromolecular Substances; D008836:Micrococcal Nuclease; D008961:Models, Structural; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D015183:Restriction Mapping; D013698:Templates, Genetic
D002843:Chromatin; D006657:Histones; D046911:Macromolecular Substances; D009707:Nucleosomes; D004247:DNA; D008836:Micrococcal Nuclease