據(jù)物理學(xué)家組織網(wǎng)報(bào)道,，生存在日本溫泉中的一種嗜熱細(xì)菌或許可解開(kāi)高等復(fù)雜生物體早期進(jìn)化的謎團(tuán)，并可能成為21世紀(jì)生物燃料生產(chǎn)的關(guān)鍵,。相關(guān)研究報(bào)告發(fā)表在《公共科學(xué)圖書(shū)館·生物學(xué)》雜志上,。
分子生物學(xué)教授艾倫·蘭博維茲介紹說(shuō)，內(nèi)含子是進(jìn)化過(guò)程中的一種神秘元素,。直到20世紀(jì)70年代,，各界都普遍認(rèn)為所有生物體內(nèi)的基因都是連續(xù)的，其由此能組成一個(gè)連續(xù)的RNA（核糖核酸）,，并可被翻譯成連續(xù)的蛋白質(zhì),。然而，包括人類(lèi)在內(nèi)的大多數(shù)高等真核生物并未遵循上述猜想,。反之,，高等生物大部分的基因都是不連續(xù)的，其由DNA（脫氧核糖核酸）編碼區(qū)域組成,，中間則由內(nèi)含子隔開(kāi),。
為了更好地了解內(nèi)含子的早期歷史，科研人員將此次的研究的重點(diǎn)放在細(xì)菌上,，因?yàn)樗麄兿嘈偶?xì)菌是內(nèi)含子進(jìn)化的源頭,。作為唯一已知的增殖原理與高等生物十分相似的細(xì)菌，科學(xué)家對(duì)細(xì)長(zhǎng)聚球藻（藻青菌的一種）著重進(jìn)行了研究,。
生物化學(xué)家格奧爾格·摩爾表示：“我們并不能回溯至10億多年前去觀察早期真核生物中的內(nèi)含子是怎樣增值的,，但我們能夠探究允許內(nèi)含子在這些生物中增殖的機(jī)理，并嘗試推斷它們?cè)谡婧松镏羞M(jìn)化的過(guò)程,。”
在對(duì)機(jī)理的研究過(guò)程中,，科學(xué)家認(rèn)定高溫在內(nèi)含子的增殖過(guò)程中扮演了關(guān)鍵的角色。如嗜熱細(xì)菌所處的溫泉,，就可解開(kāi)基因組中的DNA鏈,，使內(nèi)含子能夠更輕易地嵌入基因組中。
蘭博維茲表示,，由于地球在十多億年前正處于高溫環(huán)境,，且是早期真核生物出現(xiàn)的時(shí)段，因此DNA解鏈的證據(jù)對(duì)于設(shè)想早期真核生物如何增殖來(lái)說(shuō)具有相當(dāng)意義,。這些生物最初或許只含有小部分內(nèi)含子,，但隨著時(shí)間推移，高溫可促使內(nèi)含子快速地增殖,。
而對(duì)于細(xì)長(zhǎng)聚球藻中的內(nèi)含子進(jìn)行探索,，或許也可為利用嗜熱細(xì)菌來(lái)提升生物燃料效能的研究者提供意外的幫助。嗜熱細(xì)菌十分善于將纖維素轉(zhuǎn)化為乙醇,，但其在基因操控領(lǐng)域卻十分棘手,。而嗜熱內(nèi)含子的發(fā)現(xiàn),，可快速解決這一難題，科學(xué)家可借助Ⅱ型內(nèi)含子進(jìn)行基因標(biāo)靶,。研究人員目前已經(jīng)開(kāi)始探究能否從基因角度設(shè)計(jì)嗜熱細(xì)菌，以試圖增加纖維素生物燃料的產(chǎn)量,。(生物谷Bioon.net)
生物谷推薦原文出處：
PLoS Biol. doi:10.1371/journal.pbio.1000391
Mechanisms Used for Genomic Proliferation by Thermophilic Group II Introns
Georg Mohr1,2,3, Eman Ghanem1,2,3, Alan M. Lambowitz1,2,3*
1 Institute for Cellular and Molecular Biology, University of Texas at Austin, Austin, Texas, United States of America, 2 Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas, United States of America, 3 Section of Molecular Genetics and Microbiology, School of Biological Sciences, University of Texas at Austin, Austin, Texas, United States of America
Mobile group II introns, which are found in bacterial and organellar genomes, are site-specific retroelments hypothesized to be evolutionary ancestors of spliceosomal introns and retrotransposons in higher organisms. Most bacteria, however, contain no more than one or a few group II introns, making it unclear how introns could have proliferated to higher copy numbers in eukaryotic genomes. An exception is the thermophilic cyanobacterium Thermosynechococcus elongatus, which contains 28 closely related copies of a group II intron, constituting ~1.3% of the genome. Here, by using a combination of bioinformatics and mobility assays at different temperatures, we identified mechanisms that contribute to the proliferation of T. elongatus group II introns. These mechanisms include divergence of DNA target specificity to avoid target site saturation; adaptation of some intron-encoded reverse transcriptases to splice and mobilize multiple degenerate introns that do not encode reverse transcriptases, leading to a common splicing apparatus; and preferential insertion within other mobile introns or insertion elements, which provide new unoccupied sites in expanding non-essential DNA regions. Additionally, unlike mesophilic group II introns, the thermophilic T. elongatus introns rely on elevated temperatures to help promote DNA strand separation, enabling access to a larger number of DNA target sites by base pairing of the intron RNA, with minimal constraint from the reverse transcriptase. Our results provide insight into group II intron proliferation mechanisms and show that higher temperatures, which are thought to have prevailed on Earth during the emergence of eukaryotes, favor intron proliferation by increasing the accessibility of DNA target sites. We also identify actively mobile thermophilic introns, which may be useful for structural studies, gene targeting in thermophiles, and as a source of thermostable reverse transcriptases.
