分子生物學(xué)課件chapter7rna轉(zhuǎn)錄-資料下載頁(yè)
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【正文】 p Cys Ile In 1986, Rob Benne and his colleagues discovered that the sequence of the cytochrome oxidase(COII) mRNA from trypanosomes does not match the sequence of the COII gene. RNA editing occurs in two different situations, with different causes. sitespecific deamination guide RNAdirected uridine insertion or deletion. 1. sitespecific deamination 2. Guide RNAs direct the insertion and deletion of Uridines The mechanism of the editosome involves an endonucleolytic cut at the mismatch point between the guide RNA and the unedited transcript. The next step is catalyzed by one of the enzymes in the plex, a terminal Utransferase, which adds Us from UTP at the 3’ end of the mRNA. The opened ends are held in place by other proteins in the plex. Another enzyme, a Uspecific exoribonuclease, removes the unpaired Us. After editing has made mRNA plementary to gRNA, an RNA ligase rejoins the ends of the edited mRNA transcript. Functions of RNA edit 校正作用 調(diào)控翻譯 擴(kuò)充遺傳信息 mRNA transport Many proteins are involved in this process. Mature mRNA carries a collection of proteins that identifies it as being mRNA destined for transport . Other RNAs not only lack the particular signature collection of proteins for transport, but have their own alternative sets of proteins that actively block export. Once a RNA has been fully processed capped, spliced, and polyadenylated an mRNA is transported out of the nucleus and into the cytoplasm
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