Dewannieux Marie, Esnault Cécile, Heidmann Thierry
Unité des Rétrovirus Endogènes et Eléments Rétroïdes des Eucaryotes Supérieurs, UMR 8122 CNRS, Institut Gustave Roussy, 39 rue Camille Desmoulins, 94805 Villejuif Cedex, France.
Nat Genet. 2003 Sep;35(1):41-8. doi: 10.1038/ng1223. Epub 2003 Aug 3.
Alu elements are the most successful transposons in humans. They are 300-bp non-coding sequences transcribed by RNA polymerase III (Pol III) and are expected to retrotranspose with the aid of reverse transcriptases of cellular origin. We previously showed that human LINEs can generate cDNA copies of any mRNA transcript by means of a retroposition process involving reverse transcription and integration by the LINE-encoded endonuclease and reverse transcriptase. Here we show mobility of marked Alu sequences in human HeLa cells with the canonical features of a retrotransposition process, including splicing out of an autocatalytic intron introduced into the marked sequence, target site duplications of varying lengths and integrations into consensus A-rich sequences. We further show that the poly-A stretch at the Alu 3' end is essential for mobility, that LINEs are required for transposition and that the rate of retroposition is 100-1,000 times higher for Alu transcripts than for control mRNAs, thus accounting for the high mutational activity of these elements observed in humans.
Alu元件是人类中最成功的转座子。它们是由RNA聚合酶III（Pol III）转录的300个碱基对的非编码序列，预计会借助细胞来源的逆转录酶进行逆转座。我们之前表明，人类长散在核元件（LINEs）可以通过一个涉及逆转录以及由LINE编码的内切核酸酶和逆转录酶进行整合的逆转座过程，生成任何mRNA转录本的cDNA拷贝。在这里，我们展示了标记的Alu序列在人类HeLa细胞中的移动性，具有逆转座过程的典型特征，包括剪接去除引入标记序列中的自催化内含子、不同长度的靶位点重复以及整合到富含A的共有序列中。我们进一步表明，Alu 3'端的聚腺苷酸序列对于移动性至关重要，转座需要LINEs，并且Alu转录本的逆转座率比对照mRNA高100 - 1000倍，这就解释了在人类中观察到的这些元件的高突变活性。
