Stefanovic B, Wittop Koning T H, Schümperli D
Abteilung für Entwicklungsbiologie, Universität Bern, Switzerland.
Nucleic Acids Res. 1995 Aug 25;23(16):3152-60. doi: 10.1093/nar/23.16.3152.
The 3' processing of histone pre-mRNAs is a nuclear event in which the U7 small nuclear ribonucleoprotein (snRNP) participates as an essential trans-acting factor. We have constructed a chimeric histone-U7 RNA that when injected into the cytoplasm of Xenopus laevis oocytes assembles into a snRNP-like particle and becomes cleaved at the correct site(s). RNP assembly is a prerequisite for cleavage, but, since neither the RNA nor the RNP appreciably enter the nucleus, cleavage occurs mostly, if not exclusively, in the cytoplasm. Consistent with this, cleavage also occurs in enucleated oocytes or in oocytes which have been depleted of U7 snRNPs. Thus all necessary components for cleavage must be present in the oocyte cytoplasm. The novel cleavage occurs in cis, involving only a single molecule of chimeric RNA with its associated proteins. This reaction is equally dependent upon base pairing interactions between histone spacer sequences and the 5'-end of the U7 moiety as the natural in trans reaction. These results imply that U7 is the only snRNP required for histone RNA processing. Moreover, the chimeric RNA is expected to be useful for further studies of the cleavage and assembly mechanisms of U7 snRNP.
组蛋白前体 mRNA 的 3' 加工是一个细胞核内事件，其中 U7 小核核糖核蛋白（snRNP）作为必需的反式作用因子参与其中。我们构建了一种嵌合组蛋白 - U7 RNA，将其注射到非洲爪蟾卵母细胞的细胞质中时，它会组装成类似 snRNP 的颗粒，并在正确的位点被切割。RNP 组装是切割的前提条件，但是，由于 RNA 和 RNP 都不会明显进入细胞核，所以切割大多（如果不是全部）发生在细胞质中。与此一致的是，切割也发生在去核卵母细胞或已耗尽 U7 snRNPs 的卵母细胞中。因此，切割所需的所有必要成分必定存在于卵母细胞的细胞质中。这种新的切割是顺式发生的，仅涉及单个嵌合 RNA 分子及其相关蛋白质。该反应与天然的反式反应一样，同样依赖于组蛋白间隔序列与 U7 部分 5' 端之间的碱基配对相互作用。这些结果表明，U7 是组蛋白 RNA 加工所需的唯一 snRNP。此外，预计这种嵌合 RNA 将有助于进一步研究 U7 snRNP 的切割和组装机制。
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