Park Yongkyu, Mengus Gabrielle, Bai Xiaoying, Kageyama Yuji, Meller Victoria H, Becker Peter B, Kuroda Mitzi I
Howard Hughes Medical Institute, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA.
Mol Cell. 2003 Apr;11(4):977-86. doi: 10.1016/s1097-2765(03)00147-3.
MSL complexes bind the single male X chromosome in Drosophila to increase transcription approximately 2-fold. Complexes contain at least five proteins and two noncoding RNAs, roX1 and roX2. The mechanism of X chromosome binding is not known. Here, we identify a 110 bp sequence in roX2 characterized by high-affinity MSL binding, male-specific DNase I hypersensitivity, a shared consensus with the otherwise dissimilar roX1 gene, and conservation across species. Mutagenesis of evolutionarily conserved sequences diminishes MSL binding in vivo. MSL binding to these sites is roX RNA dependent, suggesting that complexes become competent for binding only after incorporation of roX RNAs. However, the roX RNA segments homologous to the DNA binding sites are not required, ruling out simple RNA-DNA complementarity as the primary targeting mechanism. Our results are consistent with a model in which nascent roX RNA assembly with MSL proteins is an early step in the initiation of dosage compensation.
MSL复合物结合果蝇中单一的雄性X染色体，使转录增加约2倍。该复合物至少包含五种蛋白质以及两种非编码RNA，即roX1和roX2。X染色体的结合机制尚不清楚。在此，我们在roX2中鉴定出一段110 bp的序列，其特征为与MSL具有高亲和力结合、雄性特异性的DNase I超敏反应、与差异较大的roX1基因有共同的共有序列以及跨物种保守性。对进化保守序列进行诱变会减少体内MSL的结合。MSL与这些位点的结合依赖于roX RNA，这表明复合物只有在掺入roX RNA后才具备结合能力。然而，与DNA结合位点同源的roX RNA片段并非必需，这排除了简单的RNA-DNA互补作为主要靶向机制的可能性。我们的结果与一个模型相符，即在该模型中，新生的roX RNA与MSL蛋白组装是剂量补偿起始的早期步骤。
