Albright S C, Nelson P P, Garrard W T
J Biol Chem. 1979 Feb 25;254(4):1065-73.
The relative molar ratios of each of the histone classes and protein A24 have been determined in nuclei, chromatin, and different electrophoretic forms of mono- and dinucleosomes of cultured mouse cells. For this purpose, [3H]lysine- and [14C]arginine-labeled cells were used for sample preparations, and stoichiometries were estimated from protein radioactivity profiles and known amino acid compositions following sodium dodecyl sulfate (SDS)-gel electrophoresis. The results demonstrate that upper limits of one and two histone H1 molecules exist per mono- and dinucleosome, respectively. However, isolated nuclei contain less than one copy of histone H1 per nucleosome. In addition, among the chromatin subfractions studied, histones H3, H2B, and H4 are essentially equimolar, while histone H2A is less than equimolar by 19 +/- 9%. This latter finding offers direct support to the proposal of Goldknopf (Goldknopf, I. L., French, M. F., Musso, R., and Busch, H. (1977) Proc. Natl. Acad. Sci. U. S. A. 74, 5492-5495) that protein A24 replaces histone H2A in the octamer protein core of the nucleosome, since about 10% of the total histone H2A of cultured mouse cells is in the form of protein A24 and is present in nucleosomes. From the results of the present study, it is concluded that electrophoretic fractionation of mono- and dinucleosomes is not due to variable molar ratios or amounts of the four smaller histone classes, but depends on part on DNA length, the number of associated histone H1 molecules, and non-histone chromosomal proteins.
已测定培养的小鼠细胞核、染色质以及单核小体和双核小体的不同电泳形式中各 histone 类别与蛋白质 A24 的相对摩尔比。为此，使用 [³H]赖氨酸和 [¹⁴C]精氨酸标记的细胞进行样品制备，并通过十二烷基硫酸钠（SDS）-凝胶电泳后的蛋白质放射性图谱和已知氨基酸组成来估算化学计量。结果表明，每个单核小体和双核小体分别存在一个和两个 histone H1 分子的上限。然而，分离出的细胞核中每个核小体所含的 histone H1 少于一个拷贝。此外，在所研究的染色质亚组分中，histone H3、H2B 和 H4 基本等摩尔，而 histone H2A 的摩尔数比等摩尔少 19±9%。后一发现直接支持了 Goldknopf（Goldknopf, I. L., French, M. F., Musso, R., and Busch, H. (1977) Proc. Natl. Acad. Sci. U. S. A. 74, 5492 - 5495）的提议，即蛋白质 A24 在核小体的八聚体蛋白核心中取代了 histone H2A，因为培养的小鼠细胞中约 10%的总 histone H2A 以蛋白质 A24 的形式存在于核小体中。从本研究结果得出结论，单核小体和双核小体的电泳分级分离并非由于四种较小 histone 类别的摩尔比或数量可变，而是部分取决于 DNA 长度、相关 histone H1 分子的数量以及非组蛋白染色体蛋白。
