Inoue K, Hoshijima K, Sakamoto H, Shimura Y
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Nature. 1990 Mar 29;344(6265):461-3. doi: 10.1038/344461a0.
Somatic sexual differentiation in Drosophila melanogaster is accomplished by a hierarchy of genes of which one, Sex-lethal (Sxl), is required for the functional female-specific splicing of the transcripts of the immediately downstream regulatory gene, transformer (tra). The first exon of the tra primary transcript is spliced to one of two acceptor sites. Splicing to the upstream site yields a messenger RNA which is neither sex-specific nor functional, but that produced after splicing to the downstream acceptor site yields a functional female-specific mRNA. Here we address the question of how the Sxl gene product determines the alternative splicing of tra primary transcripts. One suggestion is that non-sex-specific splicing to the upstream acceptor is blocked in female flies by sex-specific factors, but neither the identity of the female-specific factors nor the mechanism of the blockage has been specified. We have now performed co-transfection experiments in which Sxl complementary DNA and the tra gene are expressed in Drosophila Kc cells. Moreover, we find that female Sxl-encoded protein binds specifically to the tra transcript at or near the non-sex-specific acceptor site, implying that the female Sxl gene product is the trans-acting factor that regulates the alternative splicing.
果蝇的体细胞性分化是由一系列基因完成的，其中一个基因，即性致死基因（Sxl），对于紧邻其下游的调控基因transformer（tra）转录本的功能性雌性特异性剪接是必需的。tra初级转录本的第一个外显子被剪接到两个受体位点之一。剪接到上游位点产生的信使RNA既不是性别特异性的也没有功能，但剪接到下游受体位点后产生的是功能性雌性特异性mRNA。在这里，我们探讨Sxl基因产物如何决定tra初级转录本的选择性剪接这一问题。一种观点认为，雌性果蝇中，非性别特异性剪接到上游受体的过程被性别特异性因子阻断，但雌性特异性因子的身份以及阻断机制均未明确。我们现在进行了共转染实验，其中Sxl互补DNA和tra基因在果蝇Kc细胞中表达。此外，我们发现雌性Sxl编码的蛋白质在非性别特异性受体位点处或附近与tra转录本特异性结合，这意味着雌性Sxl基因产物是调节选择性剪接的反式作用因子。
