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首页> 外文期刊>Molecular and Cellular Biology >Small nuclear ribonucleoprotein (RNP) U2 contains numerous additional proteins and has a bipartite RNP structure under splicing conditions.
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Small nuclear ribonucleoprotein (RNP) U2 contains numerous additional proteins and has a bipartite RNP structure under splicing conditions.

机译：小核核糖核蛋白（RNP）U2包含许多其他蛋白质，并且在剪接条件下具有两部分RNP结构。

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Small nuclear (sn) ribonucleoprotein (RNP) U2 functions in the splicing of mRNA by recognizing the branch site of the unspliced pre-mRNA. When HeLa nuclear splicing extracts are centrifuged on glycerol gradients, U2 snRNPs sediment at either 12S (under high salt concentration conditions) or 17S (under low salt concentration conditions). We isolated the 17S U2 snRNPs from splicing extracts under nondenaturing conditions by using centrifugation and immunoaffinity chromatography and examined their structure by electron microscope. In addition to common proteins B', B, D1, D2, D3, E, F, and G and U2-specific proteins A' and B", which are present in the 12S U2 snRNP, at least nine previously unidentified proteins with apparent molecular masses of 35, 53, 60, 66, 92, 110, 120, 150, and 160 kDa bound to the 17S U2 snRNP. The latter proteins dissociate from the U2 snRNP at salt concentrations above 200 mM, yielding the 12S U2 snRNP particle. Under the electron microscope, the 17S U2 snRNPs exhibited a bipartite appearance, with two main globular domains connected by a short filamentous structure that is sensitive to RNase. These findings suggest that the additional globular domain, which is absent from 12S U2 snRNPs, contains some of the 17S U2-specific proteins. The 5' end of the RNA in the U2 snRNP is more exposed for reaction with RNase H and with chemical probes when the U2 snRNP is in the 17S form than when it is in the 12S form. Removal of the 5' end of this RNA reduces the snRNP's Svedberg value from 17S to 12S. Along with the peculiar morphology of the 17S snRNP, these data indicate that most of the 17S U2-specific proteins are bound to the 5' half of the U2 snRNA.
机译：小核（sn）核糖核蛋白（RNP）U2通过识别未剪接的pre-mRNA的分支位点在mRNA剪接中发挥作用。将HeLa核剪接提取物在甘油梯度上离心时，U2 snRNPs在12S（在高盐浓度条件下）或17S（在低盐浓度条件下）沉淀。我们通过离心和免疫亲和层析从非变性条件下的剪接提取物中分离出17S U2 snRNPs，并通过电子显微镜检查其结构。除了存在于12S U2 snRNP中的常见蛋白B'，B，D1，D2，D3，E，F和G和U2特异性蛋白A'和B”，还有至少九种先前未鉴定的蛋白分子量分别为35、53、60、66、92、110、120、150和160 kDa的分子与17S U2 snRNP结合，后一种蛋白质在盐浓度高于200 mM时从U2 snRNP上解离，产生12S U2 snRNP颗粒在电子显微镜下，17S U2 snRNPs表现出两部分的外观，两个主要的球状结构域通过对RNase敏感的短丝状结构连接在一起，这些发现表明，12S U2 snRNPs中不存在另外的球状结构域。当U2 snRNP处于17S形式时，与12S形式相比，U2 snRNP中RNA的5'端更易于与RNase H和化学探针反应。去除此RNA的5'端可使snRNP的Svedberg值从17S降至12 S.这些数据与17S snRNP的特殊形态一起表明，大多数17S U2特异性蛋白都与U2 snRNA的5'一半结合。

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