專題：Nature報(bào)道
在真核生物中，很多基因都含有一個(gè)或多個(gè)“內(nèi)含子”,，即作為mRNA一部分被轉(zhuǎn)錄、但在mRNA被翻譯成蛋白之前被除掉的序列,。在前體mRNA（pre-mRNA）中適當(dāng)位置剪接這些“內(nèi)含子”的大分子機(jī)器被稱為“剪接體”,。它由被稱為snRNPs（核內(nèi)小核糖核蛋白 ，或稱“snurps”）的幾個(gè)RNA-蛋白復(fù)合體及其他非snRNP蛋白組成,。
現(xiàn)在,，U1 snRNP（它在“內(nèi)含子”的5\'端組裝，是與一個(gè)pre-mRNA結(jié)合的第一個(gè)snurp）的結(jié)構(gòu)已被以5.5Å的分辨率確定,。由該結(jié)構(gòu)所反映的這一亞單元內(nèi)的相互作用,，顯示了“內(nèi)含子”的起始端是怎樣被U1 snRNP識(shí)別、從而使其被“剪接體”剪去的,。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 458, 475-480 (26 March 2009) | doi:10.1038/nature07851
Crystal structure of human spliceosomal U1 snRNP at 5.5 Å resolution
Daniel A. Pomeranz Krummel1,2,3, Chris Oubridge1,3, Adelaine K. W. Leung1,2, Jade Li1 & Kiyoshi Nagai1
1 MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK
2 Present addresses: Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454-9110, USA (D.A.P.K.); Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA (A.K.W.L.).
3 These authors contributed equally to this work.
Correspondence to: Kiyoshi Nagai1 Correspondence and requests for materials should be addressed to K.N.
Human spliceosomal U1 small nuclear ribonucleoprotein particles (snRNPs), which consist of U1 small nuclear RNA and ten proteins, recognize the 5' splice site within precursor messenger RNAs and initiate the assembly of the spliceosome for intron excision. An electron density map of the functional core of U1 snRNP at 5.5 Å resolution has enabled us to build the RNA and, in conjunction with site-specific labelling of individual proteins, to place the seven Sm proteins, U1-C and U1-70K into the map. Here we present the detailed structure of a spliceosomal snRNP, revealing a hierarchical network of intricate interactions between subunits. A striking feature is the amino (N)-terminal polypeptide of U1-70K, which extends over a distance of 180 ? from its RNA binding domain, wraps around the core domain consisting of the seven Sm proteins and finally contacts U1-C, which is crucial for 5'-splice-site recognition. The structure of U1 snRNP provides insights into U1 snRNP assembly and suggests a possible mechanism of 5'-splice-site recognition.
