Bouhidel K, Terzian C, Pinon H
Laboratoire de Génétique, Université Blaise Pascal, CNRS URA 360, Aubière, France.
Nucleic Acids Res. 1994 Jun 25;22(12):2370-4. doi: 10.1093/nar/22.12.2370.
The I factor of Drosophila melanogaster is a retrotransposon of the LINE superfamily. The I factor displays two non-overlapping open reading frames (ORFs) that have the potential to encode for a nucleic acid-binding protein (ORF1) and a reverse transcriptase (ORF2). Retrotransposition of the I factor has been demonstrated and a putative full-length RNA intermediate has been identified. No other transcript from functional I factor has ever been described, suggesting that the full-length RNA is also used as a messenger. Here we report that a bicistronic RNA which conserves the ORF1-ORF2 organization of the I factor transcript is a template for ORF2 translation in vivo. We further demonstrate that the first AUG of ORF2 initiates translation, but efficiency of this initiation increases approximately 200 fold when ORF1 is deleted. Our results show that the I factor transcript may be used to translate both ORFs from their own initiation codons at different rates. Various mechanisms of translation are proposed.
果蝇的I因子是LINE超家族的一种逆转座子。I因子有两个不重叠的开放阅读框（ORF），有可能编码一种核酸结合蛋白（ORF1）和一种逆转录酶（ORF2）。I因子的逆转座已得到证实，并且已鉴定出一种假定的全长RNA中间体。从未描述过功能性I因子的其他转录本，这表明全长RNA也用作信使RNA。在此我们报告，一种保留I因子转录本ORF1-ORF2组织形式的双顺反子RNA是体内ORF2翻译的模板。我们进一步证明，ORF2的第一个AUG启动翻译，但当删除ORF1时，这种起始效率会增加约200倍。我们的结果表明，I因子转录本可用于以不同速率从其自身起始密码子翻译两个ORF。文中提出了各种翻译机制。
