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Structure of recombinant rat UBF by electron image analysis and homology modelling.

机译:重组大鼠UBF的结构通过电子图像分析和同源性建模。

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摘要

We have studied the structure of recombinant rat UBF (rrUBF), an RNA polymerase I transcription factor, by electron microscopy and image analysis of single particles contrasted with methylamine tungstate. Recombinant rat UBF appeared to be a flat, U-shaped protein with a central region of low density. In the dominant projections, 2-fold mirror symmetry was seen, consistent with the dimerization properties of this molecule, and of dimensions in agreement with the length of DNA that rat UBF protects in footprinting studies. Electron microscopy of various rrUBF-DNA complexes confirmed that our recombinant protein was fully able to bind the 45S rDNA promoter, and that it caused substantial bends in the DNA. Upon extended incubation in a droplet covered by a lipid monolayer at the liquid-air interface, rrUBF formed long filamentous arrays with a railway track appearance. This structure was interpreted to consist of overlapping rrUBF dimers 3.5 nm apart, which value would represent the thickness of the protein. Our results show rrUBF to interact with and bend the promoter DNA into a roughly 10 nm diameter superhelix. Based on all these electron microscopical results, an atomic structure was predicted by homology modelling of the HMG fingers, and connected by energy minimized intervening segments.
机译:我们已经通过电子显微镜和与甲胺钨酸盐对比的单个颗粒的图像分析研究了重组大鼠UBF(rrUBF)(一种RNA聚合酶I转录因子)的结构。重组大鼠UBF似乎是一个扁平的U形蛋白,中心区域低密度。在主要的投影图中,观察到2倍镜对称性,与该分子的二聚化特性一致,并且尺寸与大鼠UBF在足迹研究中保护的DNA长度一致。各种rrUBF-DNA复合物的电子显微镜证实,我们的重组蛋白完全能够结合45S rDNA启动子,并且引起了DNA的大幅弯曲。在液-气界面上被脂质单层覆盖的液滴中进一步温育后,rrUBF形成了具有铁轨外观的长丝状阵列。该结构被解释为由相距3.5 nm的重叠rrUBF二聚体组成,该值代表蛋白质的厚度。我们的结果表明rrUBF与启动子DNA相互作用并将其弯曲成直径约10 nm的超螺旋。基于所有这些电子显微镜结果,通过HMG手指的同源性建模预测了原子结构,并通过能量最小化的中间链段进行了连接。

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