由于技术及硬件的进步，结构生物学近年来取得了一系列重要突破。然而，对于真核生物RNA剪接体(spliceosome)的结构生物学研究却一直进展缓慢。新转录出来的RNA要成为具有执行翻译功能的mRNA，需要在细胞核内经历一个非常复杂的剪切和拼接过程。这个过程是由五个小核核糖核蛋白（U1/U2/U4/U5/U6）和一系列辅助蛋白构成的巨大分子机器—剪接体执行的。小核核糖核蛋白主要由一条小核RNA和与之特异性结合的七元环蛋白复合物组成。大部分的七元环复合物是Sm 蛋白七聚体，只有在U6小核核糖核蛋白中为Lsm蛋白七聚体复合物。该申请项目计划利用结构生物学和生物化学手段，在本课题组已经取得的前期成果基础上深入研究剪接体的组装及工作机理，阐明各个小核核糖体的组装形式以及它们特异识别靶标RNA的分子基础，力图攻坚这一结构生物学领域最具挑战性的课题之一。

Important progress has been made in structural biology in recent years. Atomic or subatomic structures of many desired targets have been resolved. Nevertheless, the structural information on the physiologically significant eukaryotic spliceosome remains limited. In eukaryotes, the maturation of nascent pre-messenger RNA (mRNA) requires the removal of introns and joining of exons, a very dynamic and complex process known as splicing that is executed by spliceosome in nucleus. Spliceosome comprises five small nuclear ribonucleoproteins (snRNPs), namely U1/U2/U4/U5/U6, as well as a number of co-factors and enzymes. Each snRNP consists of one major small nuclear RNA and a specific heptameric protein complex. The heptameric ring in U6 snRNP comprises Lsm proteins, whereas the other snRNPs each contains a Sm protein ring. The Lsm heptamer specifically recognizes the 3’ fragment of U6 snRNA, assisting its binding to other components of spliceosome, and facilitating splicing of precursor messenger RNAs. In our previous study, we have determined the crystal structure of Lsm2-8 bound to a fragment of the 3’-end of U6 snRNA at 2.8 angstrom resolution and the related Lsm1-7 complex structure in 3.0 angstrom resolution. Despite the exciting progress, many important questions remain to be addressed. We aim at the structural and mechanistic understanding of the assembly and function of spliceosome. As part of the very ambitious project, we plan to focus on the study of U6 snRNP at a start. Structural and functional analysis of the assembly of U6 snRNP will offer us a great deal to the understanding of spliceosome.