Callan H G, Gall J G
Department of Embryology, Carnegie Institution of Washington, Baltimore, MD 21210.
Chromosoma. 1991 Nov;101(2):69-82. doi: 10.1007/BF00357056.
We studied the time course of [3H]-uridine incorporation into the B and C snurposomes of Xenopus oocyte nuclei. B snurposomes constitute most of the non-nucleolar granules in the 1-4 micron size range; they contain the five splicing small nuclear RNAs (snRNAs; U1, U2, U4, U5 and U6) plus a variety of associated proteins. The organelles referred to as spheres consist of a C snurposome with one or more B snurposomes on its surface. C snurposomes can exist independently of Bs and many are smaller than the structures usually classified as spheres. C snurposomes contain the trimethylguanosine moiety characteristic of snRNAs, as well as the Sm epitope found on several small nuclear ribonucleoproteins (snRNPs), but it is not known which snRNA(s) they contain. When oocytes are incubated with [3H]uridine, all of the nucleoli and chromosome loops label strongly and rapidly. By contrast, labelled RNA appears slowly in the B snurposomes and then only in a fraction of them. After a 24 h incubation, about half of the Bs are labelled, and half are unlabelled or weakly labelled. This observation suggests that there are "mature" and "immature" B snurposomes, and that only the latter acquire newly synthesized RNA. The nature of this RNA is unknown, but it probably includes the splicing snRNAs. B snurposomes on the surface of Cs also constitute a heterogeneous population, some becoming labelled and some remaining unlabelled during a 24 h incubation. An analysis of the label in "doublets" (one B and one C snurposome) suggests that RNA may pass from the Bs to the Cs.
我们研究了[3H] - 尿苷掺入非洲爪蟾卵母细胞核B型和C型剪接体的时间进程。B型剪接体构成了1 - 4微米大小范围内大部分非核仁颗粒；它们包含五种剪接小核RNA（snRNA；U1、U2、U4、U5和U6）以及多种相关蛋白。被称为球体的细胞器由一个C型剪接体及其表面的一个或多个B型剪接体组成。C型剪接体可以独立于B型剪接体存在，并且许多C型剪接体比通常归类为球体的结构更小。C型剪接体含有snRNA特有的三甲基鸟苷部分，以及在几种小核核糖核蛋白（snRNP）上发现的Sm表位，但尚不清楚它们含有哪些snRNA。当卵母细胞与[3H] - 尿苷一起孵育时，所有核仁及染色体环都迅速强烈标记。相比之下，标记的RNA在B型剪接体中出现缓慢，且仅在其中一部分中出现。孵育时长24小时后约一半的B型剪接体被标记，另一半未被标记或标记较弱。这一观察结果表明存在“成熟”和“未成熟”的B型剪接体，且只有后者获得新合成的RNA。这种RNA的性质未知，但可能包括剪接snRNA。C型剪接体表面的B型剪接体也构成了一个异质群体，在24小时孵育期间一些被标记，一些仍未被标记。对“双联体”（一个B型和一个C型剪接体）中的标记分析表明RNA可能从B型剪接体传递到C型剪接体。
