The translationally regulated msl-2 mRNP from Drosophila

果蝇的剂量补偿需要雄性特有的MSL(雄性特异性致死)复合体的表达。该复合体的MSL-2亚单位的男性特异性表达代表了剂量补偿途径中的关键差异。在雌性中，MSL-2蛋白的表达被雌性特异的RNA结合蛋白性致死(SXL)转录后抑制，SXL通过MS1-2 Pre mRNA的5‘UTR区和3’UTR区的SXL结合位点，通过整合的两步机制抑制MS1-2的表达。与5‘非编码区结合的SXL加强了内含子的保留，而内含子在雄性果蝇中被移除。当该mRNA输出到细胞质中后，与这些保留的5‘非编码区结合的SXL与与3’非编码区结合的额外的SXL协同作用，建立翻译抑制的MS1-2mRNA-蛋白质复合体(MRNP)。我们用体外转录的mRNAs和重组的SXL蛋白概括了果蝇胚胎在无细胞系统中的翻译调控。我们建议通过对重要顺式作用元件的生化分析、反式作用因子SXL的功能域以及辅助因子的鉴定来剖析沉默的mRNP。

Dosage compensation in Drosophila melanogaster requires the male-specific expression of the MSL (male-specific lethal) complex. The male-specific expression of the MSL-2 subunit of this complex represents the key difference in the dosage compensation pathway. MSL-2 protein expression is inhibited posttranscriptionally in females by the female-specific RNA binding protein Sex-Lethal (SXL), which inhibits ms1-2 expression by an integrated two step mechanism via SXL binding sites in both the 5' UTR and the 3' UTR of the ms1-2 pre mRNA. SXL binding to the 5' UTR sites enforces the retention of the intron which is removed in male flies. Following export of this mRNA into the cytoplasm, SXL bound to these retained 5' UTR sites synergizes with additional SXL bound to the 3' UTR sites to establish a translational repressed ms1-2 mRNA-protein complex (mRNP). We have recapitulated the translational regulation in a cell-free system from Drosophila embryos using in vitro transcribed mRNAs and recombinant SXL protein. We propose to dissect the silenced mRNP by biochemical analysis of functionally important cis-acting elements, the functional domains of the trans-acting factor SXL and the identification of co-factors.