1月9日，據(jù)國(guó)外媒體報(bào)道,，美國(guó)科學(xué)家最近表示,，結(jié)構(gòu)更簡(jiǎn)單的TNA也具備RNA的某些功能,，地球上的生命最初可能由幾種遺傳物質(zhì)混合組成。
除一些病毒外,，大多數(shù)生命利用DNA（脫氧核糖核酸）存儲(chǔ)信息,，利用RNA（核糖核酸）執(zhí)行由DNA編碼的指令。研究生命起源的科學(xué)家們一直認(rèn)為,，RNA既能存儲(chǔ)遺傳信息又能充當(dāng)生化酶,，使其成為一個(gè)可以開(kāi)啟生命的理想分子，因此,，RNA是地球上最先出現(xiàn)的遺傳物質(zhì),。而現(xiàn)在，科學(xué)家們表示,，TNA似乎也一樣能干——盡管人們迄今還沒(méi)有在自然界中找到它,。
美國(guó)亞利桑那州立大學(xué)的約翰-恰普特和同事已經(jīng)制造出一個(gè)TNA分子，它能折疊成三維形狀并夾有一個(gè)特殊的蛋白,。這些是制造出一個(gè)能像RNA一樣控制化學(xué)反應(yīng)的TNA酶的關(guān)鍵步驟,。他們讓TNA的各個(gè)組成成分在有一種蛋白參與的情況下進(jìn)化：三代之后出現(xiàn)了一個(gè)TNA，其擁有一個(gè)像酶一樣復(fù)雜的折疊形狀,，而且能與該蛋白結(jié)合,。
TNA與RNA、DNA的不同之處在于構(gòu)成核苷酸的糖鏈不同,，構(gòu)成TNA的糖鏈為四碳糖蘇糖,；而RNA為核糖，DNA為脫氧核糖,。TNA具備一個(gè)關(guān)鍵的優(yōu)勢(shì)：它是比核糖和脫氧核糖更小的分子,，因此更容易形成。恰普特認(rèn)為,，這并不意味著TNA是最初的遺傳物質(zhì),，早期地球的化學(xué)過(guò)程非常凌亂，最可能出現(xiàn)的場(chǎng)景是生命由不同的遺傳物質(zhì)混合而成,。
最新研究與諾貝爾化學(xué)獎(jiǎng)得主,、哈佛大學(xué)的杰克-蘇斯塔克和同事發(fā)表于《美國(guó)國(guó)家科學(xué)院院刊》的最新研究一致，蘇斯塔克團(tuán)隊(duì)制造出了一種一半是DNA,、一半是RNA的嵌合核酸,，其中的一些核酸能與目標(biāo)分子相結(jié)合。
然而,，“混合遺傳物質(zhì)組成世界”這一假設(shè)可能也存在疑問(wèn),。首先,，科學(xué)家們沒(méi)有在現(xiàn)代生物體上發(fā)現(xiàn)TNA的蹤跡,。另外,，英國(guó)劍橋大學(xué)醫(yī)學(xué)研究委員會(huì)分子生物學(xué)實(shí)驗(yàn)室的約翰·薩瑟蘭表示，盡管TNA比RNA更簡(jiǎn)單,，但我們不能確定在約40億年前,，其更容易被制造出來(lái)，因?yàn)槠襁€沒(méi)有人真正在生命出現(xiàn)前的地球環(huán)境下制造出TNA,。
恰普特也指出,，對(duì)TNA能做什么我們?nèi)匀恢跎伲驗(yàn)樽尫肿釉趯?shí)驗(yàn)室進(jìn)化的技術(shù)非常新,，這項(xiàng)研究才剛剛開(kāi)始,。（生物谷 Bioon.com）
doi:10.1073/pnas.1107113108
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Evolution of functional nucleic acids in the presence of nonheritable backbone heterogeneity
Simon G. Trevino, Na Zhanga, Mark P. Elenko, Andrej Lupták, and Jack W. Szostak
Multiple lines of evidence support the hypothesis that the early evolution of life was dominated by RNA, which can both transfer information from generation to generation through replication directed by base-pairing, and carry out biochemical activities by folding into functional structures. To understand how life emerged from prebiotic chemistry we must therefore explain the steps that led to the emergence of the RNA world, and in particular, the synthesis of RNA. The generation of pools of highly pure ribonucleotides on the early Earth seems unlikely, but the presence of alternative nucleotides would support the assembly of nucleic acid polymers containing nonheritable backbone heterogeneity. We suggest that homogeneous monomers might not have been necessary if populations of heterogeneous nucleic acid molecules could evolve reproducible function. For such evolution to be possible, function would have to be maintained despite the repeated scrambling of backbone chemistry from generation to generation. We have tested this possibility in a simplified model system, by using a T7 RNA polymerase variant capable of transcribing nucleic acids that contain an approximately 1∶1 mixture of deoxy- and ribonucleotides. We readily isolated nucleotide-binding aptamers by utilizing an in vitro selection process that shuffles the order of deoxy- and ribonucleotides in each round. We describe two such RNA/DNA mosaic nucleic acid aptamers that specifically bind ATP and GTP, respectively. We conclude that nonheritable variations in nucleic acid backbone structure may not have posed an insurmountable barrier to the emergence of functionality in early nucleic acids.
