Gebauer F, Merendino L, Hentze M W, Valcárcel J
Gene Expression Programme, European Molecular Biology Laboratory, Heidelberg, Germany.
RNA. 1998 Feb;4(2):142-50.
Male-specific expression of the protein male-specific-lethal 2 (MSL-2) controls dosage compensation in Drosophila. msl-2 gene expression is inhibited in females by Sex-lethal (SXL), an RNA binding protein known to regulate pre-mRNA splicing. An intron present at the 5' untranslated region (UTR) of msl-2 mRNA contains putative SXL binding sites and is retained in female flies. Here we show that SXL plays a dual role in the inhibition of msl-2 expression. Cotransfection of Drosophila Schneider cells with an SXL expression vector and a reporter containing the 5' UTR of msl-2 mRNA resulted in retention of the 5' UTR intron and efficient accumulation of the unspliced mRNA in the cytoplasm, where its translation was blocked by SXL, but not by the intron per se. Both splicing and translation inhibition by SXL were recapitulated in vitro and found to be dependent upon SXL binding to high-affinity sites within the intron, showing that SXL directly regulates these events. Our data reveal a coordinated mechanism for the regulation of msl-2 expression by the same regulatory factor: SXL enforces intron retention in the nucleus and subsequent translation inhibition in the cytoplasm.
蛋白质雄性特异性致死因子2（MSL-2）的雄性特异性表达控制着果蝇中的剂量补偿。msl-2基因的表达在雌性中受到性致死因子（SXL）的抑制，SXL是一种已知可调节前体mRNA剪接的RNA结合蛋白。msl-2 mRNA 5'非翻译区（UTR）存在的一个内含子含有推定的SXL结合位点，并在雌性果蝇中保留。在这里，我们表明SXL在抑制msl-2表达中起双重作用。将SXL表达载体与含有msl-2 mRNA 5'UTR的报告基因共转染果蝇施耐德细胞，导致5'UTR内含子保留，未剪接的mRNA在细胞质中有效积累，其翻译被SXL阻断，但不被内含子本身阻断。SXL对剪接和翻译的抑制在体外均得到重现，并且发现其依赖于SXL与内含子内高亲和力位点的结合，表明SXL直接调节这些事件。我们的数据揭示了由同一调节因子调控msl-2表达的协调机制：SXL在细胞核中促使内含子保留，随后在细胞质中抑制翻译。
