Department of Microbiology and Molecular Genetics, University of Vermont, Stafford Hall, Burlington, VT 05405, USA.
Structure. 2011 Mar 9;19(3):368-77. doi: 10.1016/j.str.2010.12.021. Epub 2011 Feb 3.
Cleavage factor I(m) (CFI(m)) is a highly conserved component of the eukaryotic mRNA 3' processing machinery that functions in sequence-specific poly(A) site recognition through the collaboration of a 25 kDa subunit containing a Nudix domain and a larger subunit of 59, 68, or 72 kDa containing an RNA recognition motif (RRM). Our previous work demonstrated that CFI(m)25 is both necessary and sufficient for sequence-specific binding of the poly(A) site upstream element UGUA. Here, we report the crystal structure of CFI(m)25 complexed with the RRM domain of CFI(m)68 and RNA. The CFI(m)25 dimer is clasped on opposite sides by two CFI(m)68 RRM domains. Each CFI(m)25 subunit binds one UGUA element specifically. Biochemical analysis indicates that the CFI(m)68 RRMs serve to enhance RNA binding and facilitate RNA looping. The intrinsic ability of CFI(m) to direct RNA looping may provide a mechanism for its function in the regulation of alternative poly(A) site selection.
分裂因子 I(m)（CFI(m)）是真核生物 mRNA 3' 加工机制中高度保守的组成部分，通过含有 Nudix 结构域的 25kDa 亚基和含有 RNA 识别基序（RRM）的 59、68 或 72kDa 大亚基的协作，在序列特异性多聚(A)位点识别中发挥作用。我们之前的工作表明，CFI(m)25 对于多聚(A)位点上游元件 UGUA 的序列特异性结合是必需和充分的。在这里，我们报告了 CFI(m)25 与 CFI(m)68 的 RRM 结构域和 RNA 复合物的晶体结构。CFI(m)25 二聚体被两个 CFI(m)68 RRM 结构域夹在两侧。每个 CFI(m)25 亚基特异性地结合一个 UGUA 元件。生化分析表明，CFI(m)68 的 RRM 结构域有助于增强 RNA 结合并促进 RNA 环化。CFI(m) 指导 RNA 环化的内在能力可能为其在调节替代多聚(A)位点选择中的功能提供了一种机制。
