Adolf-Butenandt-Institute and Centre for Integrated Protein Science, Ludwig-Maximilians-University, 80336 Munich, Germany.
Nucleic Acids Res. 2010 Jun;38(10):3209-21. doi: 10.1093/nar/gkq026. Epub 2010 Feb 5.
Dosage compensation in Drosophila melanogaster involves the selective targeting of the male X chromosome by the dosage compensation complex (DCC) and the coordinate, approximately 2-fold activation of most genes. The principles that allow the DCC to distinguish the X chromosome from the autosomes are not understood. Targeting presumably involves DNA sequence elements whose combination or enrichment mark the X chromosome. DNA sequences that characterize 'chromosomal entry sites' or 'high-affinity sites' may serve such a function. However, to date no DNA binding domain that could interpret sequence information has been identified within the subunits of the DCC. Early genetic studies suggested that MSL1 and MSL2 serve to recognize high-affinity sites (HAS) in vivo, but a direct interaction of these DCC subunits with DNA has not been studied. We now show that recombinant MSL2, through its CXC domain, directly binds DNA with low nanomolar affinity. The DNA binding of MSL2 or of an MSL2-MSL1 complex does not discriminate between different sequences in vitro, but in a reporter gene assay in vivo, suggesting the existence of an unknown selectivity cofactor. Reporter gene assays and localization of GFP-fusion proteins confirm the important contribution of the CXC domain for DCC targeting in vivo.
在果蝇中，剂量补偿涉及由剂量补偿复合物（DCC）有选择地靶向雄性 X 染色体，以及协调地、大约 2 倍地激活大多数基因。允许 DCC 将 X 染色体与常染色体区分开来的原则尚不清楚。靶标可能涉及 DNA 序列元件，其组合或富集标记 X 染色体。表征“染色体进入位点”或“高亲和力位点”的 DNA 序列可能具有这种功能。然而，迄今为止，在 DCC 的亚基中尚未鉴定出可以解释序列信息的 DNA 结合域。早期的遗传研究表明，MSL1 和 MSL2 有助于在体内识别高亲和力位点（HAS），但这些 DCC 亚基与 DNA 的直接相互作用尚未得到研究。我们现在表明，重组 MSL2 通过其 CXC 结构域，以低纳摩尔亲和力直接与 DNA 结合。MSL2 或 MSL2-MSL1 复合物的 DNA 结合在体外不能区分不同的序列，但在体内报告基因测定中，提示存在未知的选择性辅助因子。报告基因测定和 GFP 融合蛋白的定位证实了 CXC 结构域对体内 DCC 靶向的重要贡献。
