Jiang J, Horowitz D S, Xu R M
W. M. Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.
Proc Natl Acad Sci U S A. 2000 Mar 28;97(7):3022-7. doi: 10.1073/pnas.97.7.3022.
The splicing factor Prp18 is required for the second step of pre-mRNA splicing. We have isolated and determined the crystal structure of a large fragment of the Saccharomyces cerevisiae Prp18 that lacks the N-terminal 79 amino acids. This fragment, called Prp18Delta79, is fully active in yeast splicing in vitro and includes the sequences of Prp18 that have been evolutionarily conserved. The core structure of Prp18Delta79 is compact and globular, consisting of five alpha-helices that adopt a novel fold that we have designated the five-helix X-bundle. The structure suggests that one face of Prp18 interacts with the splicing factor Slu7, whereas the more evolutionarily conserved amino acids in Prp18 form the opposite face. The most highly conserved region of Prp18, a nearly invariant stretch of 19 aa, forms part of a loop between two alpha-helices and may interact with the U5 small nuclear ribonucleoprotein particles. The structure is consistent with a model in which Prp18 forms a bridge between Slu7 and the U5 small nuclear ribonucleoprotein particles.
剪接因子Prp18是前体mRNA剪接第二步所必需的。我们分离并确定了酿酒酵母Prp18的一个大片段的晶体结构，该片段缺少N端的79个氨基酸。这个片段称为Prp18Delta79，在体外酵母剪接中具有完全活性，并且包含Prp18中保守的序列。Prp18Delta79的核心结构紧密且呈球状，由五个α螺旋组成，它们采用了一种我们命名为五螺旋X束的新折叠方式。该结构表明Prp18的一个面与剪接因子Slu7相互作用，而Prp18中进化上更保守的氨基酸形成了相反的面。Prp18最保守的区域是一段几乎不变的19个氨基酸的序列，它形成了两个α螺旋之间的一个环的一部分，可能与U5小核核糖核蛋白颗粒相互作用。该结构与Prp18在Slu7和U5小核核糖核蛋白颗粒之间形成桥梁的模型一致。
