Plaschka Clemens, Lin Pei-Chun, Nagai Kiyoshi
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, United Kingdom.
Nature. 2017 Jun 29;546(7660):617-621. doi: 10.1038/nature22799. Epub 2017 May 22.
Intron removal requires assembly of the spliceosome on precursor mRNA (pre-mRNA) and extensive remodelling to form the spliceosome's catalytic centre. Here we report the cryo-electron microscopy structure of the yeast Saccharomyces cerevisiae pre-catalytic B complex spliceosome at near-atomic resolution. The mobile U2 small nuclear ribonucleoprotein particle (snRNP) associates with U4/U6.U5 tri-snRNP through the U2/U6 helix II and an interface between U4/U6 di-snRNP and the U2 snRNP SF3b-containing domain, which also transiently contacts the helicase Brr2. The 3' region of the U2 snRNP is flexibly attached to the SF3b-containing domain and protrudes over the concave surface of tri-snRNP, where the U1 snRNP may reside before its release from the pre-mRNA 5' splice site. The U6 ACAGAGA sequence forms a hairpin that weakly tethers the 5' splice site. The B complex proteins Prp38, Snu23 and Spp381 bind the Prp8 N-terminal domain and stabilize U6 ACAGAGA stem-pre-mRNA and Brr2-U4 small nuclear RNA interactions. These results provide important insights into the events leading to active site formation.
内含子去除需要剪接体在前体mRNA（pre-mRNA）上组装，并进行广泛重塑以形成剪接体的催化中心。在此，我们报告了酿酒酵母（Saccharomyces cerevisiae）催化前B复合物剪接体的近原子分辨率冷冻电镜结构。可移动的U2小核核糖核蛋白颗粒（snRNP）通过U2/U6螺旋II以及U4/U6双snRNP与含U2 snRNP的SF3b结构域之间的界面与U4/U6.U5三snRNP结合，该界面还与解旋酶Brr2短暂接触。U2 snRNP的3'区域灵活地附着于含SF3b的结构域，并突出于三snRNP的凹面上方，U1 snRNP在从pre-mRNA 5'剪接位点释放之前可能位于此处。U6的ACAGAGA序列形成一个发夹结构，该结构与5'剪接位点弱连接。B复合物蛋白Prp38、Snu23和Spp381结合Prp8的N端结构域，并稳定U6的ACAGAGA茎-pre-mRNA和Brr2-U4小核RNA的相互作用。这些结果为导致活性位点形成的事件提供了重要见解。
