Fury M, Andersen J, Ponda P, Aimes R, Zieve G W
Department of Pathology, SUNY Stony Brook, Stony Brook, NY 11794-8691, USA.
J Autoimmun. 1999 Mar;12(2):91-100. doi: 10.1006/jaut.1998.0266.
The small nuclear ribonucleoprotein particle (snRNP) common core proteins are the lupus-associated Sm autoantigens. In mouse fibroblasts the seven snRNP core proteins form a particle with a suggested stoichiometry of B2[D1,D2(E,F,G)2] D3. Core particle assembly occurs in the cytoplasm where newly synthesized snRNAs assemble with core proteins stored in three RNA-free complexes of (1) a 6S complex of [D1,D2(E,F,G)2] (2) a 20S complex of (B,D3 and an unidentified 70 kDa protein) and (3) a 2S-6S complex that minimally contains the B protein. In this report a panel of 13 anti-Sm monoclonal antibodies is shown to immunoprecipitate six different subsets of the cytoplasmic snRNP proteins. Four epitopes are shared by the three aforementioned complexes and five other epitopes are shared by two of the complexes. In addition, the 6S or 20S complexes are apparently disrupted by five of the antibodies. Kinetic studies show that the three cytoplasmic snRNP protein complexes have independent half-lives. These studies provide another approach for characterizing the Sm epitopes. They also complement previous in vitro snRNP assembly studies and suggest that snRNP core assembly occurs by the initial binding of snRNA to the 6S particle followed by addition of the B and D3 proteins.
小核核糖核蛋白颗粒（snRNP）的共同核心蛋白是与狼疮相关的Sm自身抗原。在小鼠成纤维细胞中，七种snRNP核心蛋白形成一种颗粒，其化学计量比推测为B2[D1,D2(E,F,G)2] D3。核心颗粒组装发生在细胞质中，新合成的snRNAs与储存在三种无RNA复合物中的核心蛋白组装在一起，这三种复合物分别是：（1）[D1,D2(E,F,G)2]的6S复合物；（2）（B、D3和一种未鉴定的70 kDa蛋白）的20S复合物；（3）至少包含B蛋白的2S - 6S复合物。在本报告中，一组13种抗Sm单克隆抗体被证明能免疫沉淀细胞质snRNP蛋白的六个不同亚组。上述三种复合物共有四个表位，另外五个表位为其中两种复合物所共有。此外，6S或20S复合物显然被其中五种抗体破坏。动力学研究表明，三种细胞质snRNP蛋白复合物具有独立的半衰期。这些研究为表征Sm表位提供了另一种方法。它们还补充了先前的体外snRNP组装研究，并表明snRNP核心组装是通过snRNA首先与6S颗粒结合，随后添加B和D3蛋白而发生的。
