SMN-independent subunits of the SMN complex - Identification of a small nuclear ribonucleoprotein assembly intermediate
SMN-independent subunits of the SMN complex - Identification of a small nuclear ribonucleoprotein assembly intermediate
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DOI：
10.1074/jbc.m702317200
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发表时间：
2007-09-21
影响因子：
4.8
通讯作者：
Dreyfuss, Gideon
中科院分区：
文献类型：
--
作者：
Battle, Daniel J.;Kasim, Mumtaz;Dreyfuss, Gideon
运动神经元 (SMN) 复合物的存活对于真核细胞中小核核糖核蛋白 (snRNP) 复合物的生物合成至关重要。 SMN水平降低会导致运动中子退行性疾病、脊髓性肌萎缩症。我们在此确定了不包含 SMN 的 SMN 复合体的稳定亚基。使用细胞提取物进行的沉降和免疫沉淀实验揭示了至少三种由 Gemin3、-4 和 -5 组成的复合物； Gemin6、-7 和 unrip；和带有 Gemin2 的 SMN，以及免费的 Gemin5。当 SMN 降低时，含有 Gemin3-Gemin4-Gemin5 和 Gemin6-Gemin7-unrip 的复合物仍保持相似的水平。在细胞中，免疫荧光显微镜显示细胞应激后 Gemin5 的差异定位。我们进一步表明，包含 Gemin5 的亚基独立于 SMN 复合物结合小核 RNA，并且不需要外源 ATP。然而，ATP 水解是从包含 Gemin5 的亚基中置换小核 RNA 并将其组装成 snRNP 所必需的。这些发现证明了 SMN 复合体的模块化性质，并确定了 snRNP 组装过程中的新中间体。
The survival of motor neurons (SMN) complex is essential for the biogenesis of small nuclear ribonucleoprotein (snRNP) complexes in eukaryotic cells. Reduced levels of SMN cause the motor neutron degenerative disease, spinal muscular atrophy. We identify here stable subunits of the SMN complex that do not contain SMN. Sedimentation and immunoprecipitation experiments using cell extracts reveal at least three complexes composed of Gemin3, -4, and -5; Gemin6, -7, and unrip; and SMN with Gemin2, as well as free Gemin5. Complexes containing Gemin3-Gemin4-Gemin5 and Gemin6-Gemin7-unrip persist at similar levels when SMN is reduced. In cells, immunofluorescence microscopy shows differential localization of Gemin5 after cell stress. We further show that the Gemin5-containing subunits bind small nuclear RNA independently of the SMN complex and without a requirement for exogenous ATP. ATP hydrolysis is, however, required for displacement of small nuclear RNAs from the Gemin5-containing subunits and their assembly into snRNPs. These findings demonstrate a modular nature of the SMN complex and identify a new intermediate in the snRNP assembly process.