Structural Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA.
Structure. 2010 Feb 10;18(2):216-27. doi: 10.1016/j.str.2009.12.009.
The 5' guanine-N7 cap is the first cotranscriptional modification of messenger RNA. In Saccharomyces cerevisiae, the first two steps in capping are catalyzed by the RNA triphosphatase Cet1 and RNA guanylyltransferase Ceg1, which form a complex that is directly recruited to phosphorylated RNA polymerase II (RNAP IIo), primarily via contacts between RNAP IIo and Ceg1. A 3.0 A crystal structure of Cet1-Ceg1 revealed a 176 kDa heterotetrameric complex composed of one Cet1 homodimer that associates with two Ceg1 molecules via interactions between the Ceg1 oligonucleotide binding domain and an extended Cet1 WAQKW amino acid motif. The WAQKW motif is followed by a flexible linker that would allow Ceg1 to achieve conformational changes required for capping while maintaining interactions with both Cet1 and RNAP IIo. The impact of mutations as assessed through genetic analysis in S. cerevisiae is consonant with contacts observed in the Cet1-Ceg1 structure.
5' 鸟嘌呤-N7 帽是信使 RNA 的第一个共转录修饰。在酿酒酵母中,帽结构形成的前两步由 RNA 三磷酸酶 Cet1 和 RNA 鸟苷转移酶 Ceg1 催化,它们形成一个复合物,主要通过 RNA 聚合酶 II(RNAP IIo)和 Ceg1 之间的相互作用,直接被招募到磷酸化的 RNAP IIo 上。Cet1-Ceg1 的 3.0A 晶体结构揭示了一个由 176 kDa 的异四聚体组成的复合物,由一个 Cet1 同源二聚体组成,该二聚体通过 Ceg1 寡核苷酸结合结构域和延伸的 Cet1 WAQKW 氨基酸模体之间的相互作用与两个 Ceg1 分子结合。WAQKW 模体后面是一个柔性接头,该接头允许 Ceg1 实现帽结构形成所需的构象变化,同时保持与 Cet1 和 RNAP IIo 的相互作用。通过在酿酒酵母中的遗传分析评估突变的影响与在 Cet1-Ceg1 结构中观察到的相互作用一致。