延伸体（elongator）是一个多蛋白复合物，由Elp1-3及Elp4-6两种亚复合体组成。研究表明，延伸体在酵母和人类中是高度保守的，它在RNA聚合酶II介导的转录延伸及其它许多过程（比如细胞骨架构建、胞外分泌以及tRNA修饰）中起到了重要作用。
2012年2月，来自EMBL和IGBMC的科学家研究了延伸体蛋白中的三种蛋白，即Elp4，Elp5和Elp6，他们已经发现这三种蛋白不只是简单地堆积在一起产生三蛋白组(trio)，而且两种相同的三蛋白组发生联合形成一种环。详见：Nature子刊：延伸体复合物环状结构有助确保蛋白准确产生。
近日，来自南开大学龙加福教授的课题组确定了酵母Elp4-6亚复合体的晶体结构,阐明了延伸体复合物的装配及其底物识别机制。相关论文发表在5月2日的The Journal of Biological Chemistry。
分析Elp4-6的晶体结构得知，Elp6作为了一个“桥”来连接Elp4和Elp5。详尽的结构及序列分析表明，Elp4-6亚复合体的每一个亚基都形成了一个RecA-ATPase样的折叠，但是这些结构没有ATPases的核心序列特征。
定点突变及生化分析表明，Elp4-6亚复合体能够在体外及体内形成六聚体环状结构。
此外，GST pull-down分析显示，Elp4-6的环状结构对于它特异性的与组蛋白H3的结合是非常重要的。（生物谷Deepblue编译）
doi: 10.1074/jbc.M112.341560
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Crystal structure of the elongator subcomplex Elp4-6
Zhijie Lin, Weijing Zhao, Wentao Diao, Xingqiao Xie, Zheng Wang, Jinxiu Zhang, Yuequan Shen and Jiafu Long.
Elongator is a multiprotein complex composed of two subcomplexes, Elp1-3 and Elp4-6. Elongator is highly conserved between yeast and humans and plays an important role in RNA polymerase II-mediated transcriptional elongation and many other processes, including cytoskeleton organization, exocytosis, and tRNA modification.Here, we determined the crystal structure of the Elp4-6 subcomplex of yeast. The overall structure of Elp4-6 revealed that Elp6 acts as a bridge to assemble Elp4 and Elp5.Detailed structural and sequence analyses revealed that each subunit in the Elp4-6 subcomplex forms a RecA-ATPase-like fold although it lacks the key sequence signature of ATPases.Site-directed mutagenesis and biochemical analyses indicated that the Elp4-6 subcomplex can assemble into a hexameric ring-shaped structure in vitro and in vivo.Furthermore, GST pull-down assays showed that the ring-shaped assembly of the Elp4-6 subcomplex is important for its specific histone H3 binding. Our results may shed light on the substrate recognition and assembly of the holo-Elongator complex.
