小干擾型RNA(small interfering RNAs, siRNAs)所引發的RNA干擾現象(RNA interference, RNAi)，能夠具有專一性的沉默目標mRNA。然而，利用RNAi的技術，降低對細胞所必需基因的表現，可能會導致細胞停止生長或細胞死亡。由於這些因素，使得RNAi的應用受到限制，包括對於基因功能上的長期研究。而一個可誘發的RNAi表現系統，將可以克服這些限制。當我們能夠嚴謹的調控shRNA產生時，將有助於研究當破壞細胞某些重要基因時，是否會造成明顯的表現型，尤其是在細胞發育或細胞分化時期。因此，我們設計一種可誘發的shRNAs表現系統，而藉著RNAi的作用，可以讓我們控制特定基因之表現。首先，我們構築數種以人類H1起動子為骨架的質體，並且在起動子內外放置操縱子序列，而這些操縱子序列是來自大腸桿菌乳糖操縱組(lac operon)。在這個可誘發的shRNAs表現系統中，當沒有IPTG存在時，乳糖抑制子會結合到起動子上的操縱子序列，藉此阻礙起動子進行轉錄作用。此外，我們也將操縱子序列構築於起動子的不同位置，以測試何種組合的調控能力最佳。而在實驗中，我們以luciferase基因和p53基因當做目標基因，以測試系統的沉默效率。結果發現：當我們未加入IPTG時，實驗組的目標基因表現量為對照組的60%；處理IPTG後，目標基因的表現量降到5%。因此，乳糖抑制子的確會結合到操縱子序列，藉此阻礙起動子進行轉錄作用，而且誘發反應可被IPTG調控。但是，在我們的系統中，卻有高背景值的問題，代表即使沒有IPTG存在，仍然會降低目標基因的表現。為了改善背景值的問題，我們設計另一種可誘發的的siRNAs表現系統，此系統是以兩個修飾過的起動子為基礎，並且各自轉錄正義股RNA與反義股RNA，最後形成siRNAs。經過測試，在這個系統中，當沒有IPTG存在時，乳糖抑制子會結合到起動子上的操縱子序列，並且阻礙起動子進行轉錄作用，無法產生siRNAs，使得目標基因的表現完全正常；處理IPTG之後，目標基因的表現量降到剩15%。接著，我們以幼倉鼠腎細胞(BHK cell)為研究模型，成功的證明可誘發的siRNAs表現系統的調控能力。總而言之，我們所設計的可誘發的RNAi表現系統，可以廣泛的應用在對於基因功能或治療應用之基礎研究。

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