Kunkel G R, Martinson H G
Nucleic Acids Res. 1981 Dec 21;9(24):6869-88. doi: 10.1093/nar/9.24.6869.
We have been unable to "force" double-stranded RNA to fold into nucleosome-like structures using several different histone-RNA "reconstitution" procedures. Even if the histones are first stabilized in octameric form by dimethylsuberimidate cross-linking they are still unable to form specific complexes with the RNA. Moreover double-stranded RNA is unable to induce histones to assemble into octamers although we confirm that the non-nucleic acid homopolymer, polyglutamic acid, has this ability. We have also determined, using pyrimidine tract analysis, that nucleosomes will not form over a sufficiently long segment of poly(dA).poly(dT) in a recombinant DNA molecule. Thus nucleosomes cannot fold DNA containing an 80 base pair poly(dA).poly(dT) segment but a 20 base pair segment can be accommodated in nucleosomes fairly well. Segments of intermediate length can be accommodated but are clearly selected against. Poly(dA).poly(dT) differs only slightly from natural DNA in helix structure. Therefore either this homopolymer resists folding, or nucleosomes are very exacting in the nucleic acid steroid parameters they will tolerate. Such constraints may be relevant to nucleosome positioning in chromatin.
我们一直无法通过几种不同的组蛋白 - RNA“重组”程序，“迫使”双链RNA折叠成核小体样结构。即使组蛋白首先通过亚氨二甲酸二甲酯交联稳定成八聚体形式，它们仍然无法与RNA形成特定复合物。此外，双链RNA无法诱导组蛋白组装成八聚体，尽管我们证实非核酸同聚物聚谷氨酸具有这种能力。我们还使用嘧啶序列分析确定，在重组DNA分子中，核小体不会在足够长的聚（dA）·聚（dT）片段上形成。因此，核小体无法折叠包含80个碱基对聚（dA）·聚（dT）片段的DNA，但20个碱基对的片段可以较好地容纳在核小体中。中等长度的片段可以被容纳，但明显受到排斥。聚（dA）·聚（dT）在螺旋结构上与天然DNA仅有细微差别。因此，要么这种同聚物抵抗折叠，要么核小体对它们所能容忍的核酸参数要求非常严格。这些限制可能与染色质中核小体的定位有关。
