轉(zhuǎn)座子是一些小片段DNA,，它們能在一個細(xì)胞的基因組中移動,，在這個過程中急劇的增加了基因組的大小。多年以來,，研究人員一直認(rèn)為這種DNA是沒有任何作用的“垃圾”,，對其知之甚少。然而最新的發(fā)現(xiàn)卻揭開了轉(zhuǎn)座子那變幻莫測的神奇世界,。格魯吉亞大學(xué)的科學(xué)家發(fā)現(xiàn)基因功能的自然選擇在不斷的推動著一種LTR逆轉(zhuǎn)座子（LTR-R）的進(jìn)化,。LTR-R是轉(zhuǎn)座子的一個子類，它在植物中數(shù)目尤其眾多,，可通過反轉(zhuǎn)錄實現(xiàn)復(fù)制（RNA介導(dǎo)復(fù)制）,。
研究人員分析了水稻LTR-R基因的遺傳變異模式，從而研究可能限制核基因組擴(kuò)增和數(shù)目的選擇性壓力類型,。他們發(fā)現(xiàn)LTR-R高度純化選擇參與自身復(fù)制和生命周期的基因,，因而受到嚴(yán)重的進(jìn)化限制。研究人員還發(fā)現(xiàn),，不管LTR-R序列屬于哪一家族,，它們均表現(xiàn)出相似的“生活史”。
首席研究員Regina Baucom說：“科學(xué)家的這些發(fā)現(xiàn)有助于解釋為什么這些遺傳因素能在沉寂了數(shù)百萬年后還能突然在基因組內(nèi)擴(kuò)增,，它們不會導(dǎo)致更多的長期傷害,，而是占據(jù)基因組內(nèi)的空間。”（生物谷Bioon.com）
生物谷推薦原始出處：
Genome Research Published in Advance November 24, 2008, doi: 10.1101/gr.083360.108 Genome Res. 2009.
Natural selection on gene function drives the evolution of LTR retrotransposon families in the rice genome
Regina S. Baucom13, James C. Estill2, Jim Leebens-Mack2 and Jeffrey L. Bennetzen1
1Department of Genetics, University of Georgia, Athens, Georgia 30602-7223, USA
2Plant Biology Department, University of Georgia, Athens, Georgia 30602-7223, USA
Although the proliferation of LTR retrotransposons can cause major genomic modification and reorganization, the evolutionary dynamics that affect their frequency in host genomes are poorly understood. We analyzed patterns of genetic variation among LTR retrotransposons from Oryza sativa to investigate the type of selective forces that potentially limit their amplification and subsequent population of a nuclear genome. We performed both intra- and interfamily analyses of patterns of molecular sequence variation across multiple LTR retrotransposon genes. This analysis involved more than 1000 LTR retrotransposon sequences from 14 separate families that varied in both their insertion dates and full-length copy numbers. We uncovered evidence of strong purifying selection across all gene regions, but also indications that rare episodes of positive selection and adaptation to the host genome occur. Furthermore, our results indicate that LTR retrotransposons exhibit different but predictable patterns of sequence variation depending on their date of transposition, suggesting that LTR retrotransposons, regardless of superfamily and family classifications, show similar “life-histories.”
