Department of Microbiology and Molecular Genetics, The Markey Center for Molecular Genetics, University of Vermont, Burlington, VT, USA.
RNA Biol. 2011 Sep-Oct;8(5):748-53. doi: 10.4161/rna.8.5.16040. Epub 2011 Sep 1.
3'-end cleavage and subsequent polyadenylation are critical steps in mRNA maturation. The precise location where cleavage occurs (referred to as poly(A) site) is determined by a tripartite mechanism in which a A(A/U)UAAA hexamer, GU rich downstream element and UGUA upstream element are recognized by the cleavage and polyadenylation factor (CPSF), cleavage stimulation factor (CstF) and cleavage factor I(m) (CFI(m)), respectively. CFI(m) is composed of a smaller 25 kDa subunit (CFI(m)25) and a larger 59, 68 or 72 kDa subunit. CFI(m)68 interacts with CFI(m)25 through its N-terminal RNA recognition motif (RRM). We recently solved the crystal structures of CFI(m)25 bound to RNA and of a complex of CFI(m)25, the RRM domain of CFI(m)68 and RNA. Our study illustrated the molecular basis for UGUA recognition by the CFI(m) complex, suggested a possible mechanism for CFI(m) mediated alternative polyadenylation, and revealed potential links between CFI(m) and other mRNA processing factors, such as the 20 kDa subunit of the cap binding protein (CBP20), and the splicing regulator U2AF65.
3'-末端切割和随后的多聚腺苷酸化是 mRNA 成熟的关键步骤。切割发生的确切位置（称为多聚（A）位点）由三部分机制决定，其中 A(A/U)UAAA 六聚体、富含 GU 的下游元件和 UGUA 上游元件分别被切割和多聚腺苷酸化因子（CPSF）、切割刺激因子（CstF）和切割因子 I(m)（CFI(m)）识别。CFI(m)由较小的 25 kDa 亚基（CFI(m)25）和较大的 59、68 或 72 kDa 亚基组成。CFI(m)68 通过其 N 端 RNA 识别基序（RRM）与 CFI(m)25 相互作用。我们最近解决了 CFI(m)25 与 RNA 结合的晶体结构以及 CFI(m)25、CFI(m)68 的 RRM 结构域和 RNA 的复合物的晶体结构。我们的研究说明了 CFI(m) 复合物识别 UGUA 的分子基础，提出了 CFI(m) 介导的可变多聚腺苷酸化的可能机制，并揭示了 CFI(m) 与其他 mRNA 加工因子之间的潜在联系，如帽子结合蛋白 (CBP20) 的 20 kDa 亚基和剪接调节因子 U2AF65。
