生物谷報道:加州大學Santa Cruz分校的研究者確定了一種RNA酶或“核酶”的三維結(jié)構(gòu),，它執(zhí)行著合成新RNA分子所需的基礎(chǔ)反應(yīng),。他們的結(jié)果提供了探尋在數(shù)十億年前生命出現(xiàn)的進化道路上出現(xiàn)的最早的自我復(fù)制分子的途徑,。
在目前所有已知的生命形式中,，DNA和RNA分子的合成都是由蛋白質(zhì)構(gòu)成的酶完成,。而合成這些蛋白的指令又包含在DNA或RNA（核酸）組成的基因中,。這一循環(huán)的過程向生命起源理論提出了挑戰(zhàn),。“誰先出現(xiàn),，是核酸還是蛋白質(zhì)？這個問題似乎是個無法解決的悖論,。但是隨著核酶的發(fā)現(xiàn),，現(xiàn)在我們能構(gòu)想出一個生物前的‘RNA世界’，其中自我復(fù)制的核酶同時完成了兩項任務(wù),。”William Scott說,，他是加州大學Santa Cruz分校的化學和生物化學副教授。
Scot和博士后研究員Michael Robertson確定了一種核酶的結(jié)構(gòu),，它能將兩個RNA的亞單位結(jié)合起來,，這一反應(yīng)與生物系統(tǒng)中稱為RNA多聚酶的蛋白完成的反應(yīng)相同。他們的發(fā)現(xiàn)發(fā)表在3月16日一期的《科學》雜志中,。“RNA依賴的RNA多聚酶核酶是整個RNA世界假說的基礎(chǔ),。” Robertson說，“通過它，你將能得到一個可以自我復(fù)制的RNA,；在某些拷貝中出現(xiàn)的突變或錯誤導(dǎo)致的變異將受到達爾文自然選擇的作用,，這種分子就會進化成更大更好的核酶。這就是這一結(jié)構(gòu)如此吸引人的原因,。”Robertson和Scott確定結(jié)構(gòu)的核酶并不是一個能完全自我復(fù)制的RNA分子,，但是它的確能實現(xiàn)作為“連接酶”將兩個RNA亞單位連接起來的基礎(chǔ)反應(yīng)。
Fig. 1. Ligation reaction and L1 ligase secondary structures. (A) Ligation reaction catalyzed by the L1 ligase in which the 3'-hydroxyl of the 3'-terminal residue of the substrate oligonucleotide attacks the -phosphorus of the ribozyme's 5'-terminal guanosine triphosphate, which creates a new phosphodiester bond. (B) The proposed secondary structure of the full-length L1 ribozyme. Nucleotides in lowercase are derived from the constant-sequence regions of the original N90 library; uppercase residues are derived from the randomized region of the pool. The substrate oligonucleotide is italicized. Positions within shaded boxes were invariant among clones isolated from a mutagenized reselection of the L1 ligase; positions in boldface were conserved in >85% of isolated clones. The dotted line indicates a base triple. [Figure adapted from (9).] (C) The secondary structure of the minimized crystallization construct, L1X6c
原文出處:
Science 16 March 2007 Vol 315, Issue 5818, Pages 1461-1610
The Structural Basis of Ribozyme-Catalyzed RNA Assembly
Michael P. Robertson and William G. Scott
Science 16 March 2007: 1549-1553.
A synthetic ribozyme catalyzes the bond formation necessary for RNA synthesis by transition-state stabilization and acid-base catalysis, perhaps as in an early RNA world.
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作者簡介:
William Scott's home page and links
