生物谷報(bào)道：啟動(dòng)環(huán)（trigger loop,，TL）結(jié)構(gòu)是真核生物和原核生物RNA聚合酶中的一個(gè)高度保守區(qū)域,，但它在轉(zhuǎn)錄過程的確切功能目前還不甚了解。美國斯坦福大學(xué)的Kaplan等人的最新研究發(fā)現(xiàn),，TL在底物選擇過程中發(fā)揮重要功能,，是真菌毒素α鵝膏覃堿（α-amanitin）的直接作用位點(diǎn)。該研究結(jié)果發(fā)表于6月5日的《分子細(xì)胞》（Molecular Cell）上,。
以往研究表明,，TL結(jié)構(gòu)直接與新合成RNA的3'端和NTP相互作用，其中一個(gè)保守的組氨酸殘基直接與NTP底物相結(jié)合,。Kaplan等人用其他氨基酸替代釀酒酵母RNA聚合酶Ⅱ中TL結(jié)構(gòu)中的His1085殘基,，結(jié)果導(dǎo)致釀酒酵母表現(xiàn)出嚴(yán)重的生長缺陷，甚至無法存活,。離體實(shí)驗(yàn)表明，His1085能夠選擇正確的NTP底物,，該位點(diǎn)變異后,，聚合酶Ⅱ摻入錯(cuò)誤的NTP底物和2'dNTP底物的可能性大大增加。
α鵝膏覃堿能夠抑制RNA聚合酶Ⅱ的延伸速率,，降低其底物選擇性,，但His1085被替代后的RNA聚合酶Ⅱ?qū)?alpha;鵝膏覃堿則具有較高的抗性。研究人員進(jìn)一步研究了純化的RNA聚合酶－α鵝膏覃堿復(fù)合體的晶體結(jié)構(gòu),，發(fā)現(xiàn)α鵝膏覃堿和TL結(jié)構(gòu)間存在直接的相互作用,。因此，研究人員認(rèn)為,，α鵝膏覃堿通過直接作用于TL結(jié)構(gòu)而降低RNA聚合酶Ⅱ的速率和保真度,。（生物谷www.bioon.com）
生物谷推薦原始出處：
Molecular Cell，Vol 30, 547-556, 05 June 2008,，Craig D. Kaplan, Roger D. Kornberg
The RNA Polymerase II Trigger Loop Functions in Substrate Selection and Is Directly Targeted by α-Amanitin
Craig D. Kaplan,1, Karl-Magnus Larsson,1 and Roger D. Kornberg1
1 Department of Structural Biology, Stanford University, Stanford, CA 94305, USA
Corresponding author
Summary
Structural, biochemical, and genetic studies have led to proposals that a mobile element of multisubunit RNA polymerases, the Trigger Loop (TL), plays a critical role in catalysis and can be targeted by antibiotic inhibitors. Here we present evidence that the Saccharomyces cerevisiae RNA Polymerase II (Pol II) TL participates in substrate selection. Amino acid substitutions within the Pol II TL preferentially alter substrate usage and enzyme fidelity, as does inhibition of transcription by α-amanitin. Finally, substitution of His1085 in the TL specifically renders Pol II highly resistant to α-amanitin, indicating a functional interaction between His1085 and α-amanitin that is supported by rerefinement of an α-amanitin-Pol II crystal structure. We propose that α-amanitin-inhibited Pol II elongation, which is slow and exhibits reduced substrate selectivity, results from direct α-amanitin interference with the TL.
