Verdone Loredana, Galardi Silvia, Page David, Beggs Jean D
Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3JR, United Kingdom.
Curr Biol. 2004 Aug 24;14(16):1487-91. doi: 10.1016/j.cub.2004.08.032.
Lsm proteins are ubiquitous, multifunctional proteins that affect the processing of most RNAs in eukaryotic cells, but their function is unknown. A complex of seven Lsm proteins, Lsm2-8, associates with the U6 small nuclear RNA (snRNA) that is a component of spliceosome complexes in which pre-mRNA splicing occurs. Spliceosomes contain five snRNAs, U1, U2, U4, U5, and U6, that are packaged as ribonucleoprotein particles (snRNPs). U4 and U6 snRNAs contain extensive sequence complementarity and interact to form U4/U6 di-snRNPs. U4/U6 di-snRNPs associate with U5 snRNPs to form U4/U6.U5 tri-snRNPs prior to spliceosome assembly. Within spliceosomes, disruption of base-paired U4/U6 heterodimer allows U6 snRNA to form part of the catalytic center. Following completion of the splicing reaction, snRNPs must be recycled for subsequent rounds of splicing, although little is known about this process. Here we present evidence that regeneration of splicing activity in vitro is dependent on Lsm proteins. RNP reconstitution experiments with exogenous U6 RNA show that Lsm proteins promote the formation of U6-containing complexes and suggest that Lsm proteins have a chaperone-like function, supporting the assembly or remodeling of RNP complexes involved in splicing. Such a function could explain the involvement of Lsm proteins in a wide variety of RNA processing pathways.
Lsm蛋白是普遍存在的多功能蛋白，影响真核细胞中大多数RNA的加工过程，但其功能尚不清楚。由七种Lsm蛋白组成的复合物Lsm2 - 8与U6小核RNA（snRNA）结合，U6 snRNA是剪接体复合物的组成部分，前体mRNA剪接在此复合物中发生。剪接体包含五种snRNA，即U1、U2、U4、U5和U6，它们被包装成核糖核蛋白颗粒（snRNP）。U4和U6 snRNA含有广泛的序列互补性并相互作用形成U4 / U6双snRNP。在剪接体组装之前，U4 / U6双snRNP与U5 snRNP结合形成U4 / U6·U5三snRNP。在剪接体内，碱基配对的U4 / U6异二聚体的破坏使U6 snRNA形成催化中心的一部分。剪接反应完成后，snRNP必须被循环利用以进行后续的剪接轮次，尽管对此过程了解甚少。在这里，我们提供证据表明体外剪接活性的再生依赖于Lsm蛋白。用外源U6 RNA进行的RNP重组实验表明，Lsm蛋白促进含U6复合物的形成，并表明Lsm蛋白具有类似分子伴侣的功能，支持参与剪接的RNP复合物的组装或重塑。这样的功能可以解释Lsm蛋白参与多种RNA加工途径的原因。
