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近日，Plant Cell雜誌在線發表題為「 Intron DNA sequences can be more important than the proximal promoter in determining the site of transcript initiation 」 的研究論文， 揭示內含子將比啟動子更能決定基因的轉錄起始位點。
Figure 3. Introns stimulates expression of in the absence of a Proximal Promoter
雖然內含子對翻譯產物無實際意義，但有研究表明它同樣發揮著重要作用，比如：與前體mRNA的選擇性剪切有關，從而使得一個基因可以產生多種不同轉錄產物，進而翻譯成不同的蛋白質。近年來，越來越多的證據表明內含子對於基因的表達具有調控作用。
該文章研究人員以擬南芥中UBQ10基因的內含子作為研究對象，將該內含子插入報告基因TRP1:GUS表達盒轉錄起始位點（TSS）周圍6個不同位置，通過分析GUS基因表達的強弱的結果表明（1）除了在TSS上遊5』端較遠的位置外，內含子處於TSS周圍都能夠增強基因的表達；（2）當內含子處於5』-UTR區域時，TSS會發生改變；（3）當內含子存在時，即使刪除了啟動子的關鍵區域，基因的表達仍然可以維持；（4）即使啟動子存在，TSS也會隨著內含子的位置不同而發生改變。這些新發現的內含子的功能不僅有助於深化我們對於基因轉錄調控機制的認識，而且能夠為以增強外源基因表達為目的的基因表達盒的設計提供新的方法。
Intron DNA Sequences Can Be More Important Than the Proximal Promoter in Determining the Site of Transcript Initiation.
Gallegos JE, Rose AB.
To more precisely define the positions from which certain intronic regulatory sequences increase mRNA accumulation, the effect of a UBIQUITIN intron on gene expression was tested from 6 different positions surrounding the transcription start site (TSS) of a reporter gene fusion inArabidopsis thaliana. The intron increased expression from all transcribed positions, but had no effect when upstream of the 5'-most TSS. While this implies that the intron must be transcribed to increase expression, the TSS changed when the intron was located in the 5' UTR, suggesting that the intron affects transcription initiation. Remarkably, deleting 303 nt of the promoter including all known TSSs and all but 18 nt of the 5'-UTR had virtually no effect on the level of gene expression as long as an intron containing stimulatory sequences was included. Instead, transcription was initiated in normally untranscribed sequences the same distance upstream of the intron as when the promoter was intact. These results suggest that certain intronic DNA sequences play unexpectedly large roles in directing transcription initiation and constitute a previously unrecognized type of downstream regulatory element for genes transcribed by RNA polymerase II.
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