Lorenzen Kristina, Vannini Alessandro, Cramer Patrick, Heck Albert J R
Department of Biomolecular Mass Spectrometry, Bijvoet Center for Biomolecular Research and Utrecht Institute for Chemistry, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands.
Structure. 2007 Oct;15(10):1237-45. doi: 10.1016/j.str.2007.07.016.
RNA polymerases (Pol) II and III synthesize eukaryotic mRNAs and tRNAs, respectively. The crystal structure of the 12 subunit Pol II is known, but only limited structural information is available for the 17 subunit Pol III. Using mass spectrometry (MS), we correlated masses of Pol II complexes with the Pol II structure. Analysis of Pol III showed that the complete enzyme contains a single copy of each subunit and revealed a 15 subunit form lacking the Pol III-specific subcomplex C53/37. DMSO treatment dissociated the C17/25 heterodimer of Pol III, confirming a peripheral location as its counterpart in Pol II. Tandem MS revealed the Pol III-specific subunits C82 and C34 dissociating as a heterodimer. C11 was retained, arguing against a stable trimeric subcomplex, C53/37/11. These data suggest that Pol III consists of a 10 subunit Pol II-like core; the peripheral heterodimers C17/25, C53/37, and C82/34; and subunit C31, which bridges between C82/34, C17/25, and the core.
RNA聚合酶（Pol）II和III分别负责合成真核生物的信使核糖核酸（mRNA）和转运核糖核酸（tRNA）。12个亚基的Pol II的晶体结构已为人所知，但对于17个亚基的Pol III，仅获得了有限的结构信息。我们利用质谱法（MS），将Pol II复合物的质量与Pol II的结构关联起来。对Pol III的分析表明，完整的酶每个亚基仅含一个拷贝，并揭示了一种缺少Pol III特异性亚复合物C53/37的15亚基形式。二甲基亚砜（DMSO）处理使Pol III的C17/25异二聚体解离，证实了其在Pol II中对应物的外围位置。串联质谱显示，Pol III特异性亚基C82和C34作为异二聚体解离。C11保留下来，这与稳定的三聚体亚复合物C53/37/11不符。这些数据表明，Pol III由一个10亚基的类Pol II核心、外围异二聚体C17/25、C53/37和C82/34，以及在C82/34、C17/25和核心之间起桥梁作用的亚基C31组成。
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