Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, U.S.A.
Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, U.S.A.
Biochem Soc Trans. 2021 Nov 1;49(5):2229-2240. doi: 10.1042/BST20210323.
In animal cells, replication-dependent histone mRNAs end with a highly conserved stem-loop structure followed by a 4- to 5-nucleotide single-stranded tail. This unique 3' end distinguishes replication-dependent histone mRNAs from all other eukaryotic mRNAs, which end with a poly(A) tail produced by the canonical 3'-end processing mechanism of cleavage and polyadenylation. The pioneering studies of Max Birnstiel's group demonstrated nearly 40 years ago that the unique 3' end of animal replication-dependent histone mRNAs is generated by a distinct processing mechanism, whereby histone mRNA precursors are cleaved downstream of the stem-loop, but this cleavage is not followed by polyadenylation. The key role is played by the U7 snRNP, a complex of a ∼60 nucleotide U7 snRNA and many proteins. Some of these proteins, including the enzymatic component CPSF73, are shared with the canonical cleavage and polyadenylation machinery, justifying the view that the two metazoan pre-mRNA 3'-end processing mechanisms have a common evolutionary origin. The studies on U7 snRNP culminated in the recent breakthrough of reconstituting an entirely recombinant human machinery that is capable of accurately cleaving histone pre-mRNAs, and determining its structure in complex with a pre-mRNA substrate (with 13 proteins and two RNAs) that is poised for the cleavage reaction. The structure uncovered an unanticipated network of interactions within the U7 snRNP and a remarkable mechanism of activating catalytically dormant CPSF73 for the cleavage. This work provides a conceptual framework for understanding other eukaryotic 3'-end processing machineries.
在动物细胞中，复制依赖性组蛋白 mRNA 以高度保守的茎环结构结尾，然后是 4 到 5 个核苷酸的单链尾巴。这种独特的 3' 端将复制依赖性组蛋白 mRNA 与所有其他真核 mRNA 区分开来，后者的 3' 端由经典的切割和多聚腺苷酸化 3'-末端加工机制产生的聚（A）尾巴。Max Birnstiel 小组的开创性研究近 40 年前证明，动物复制依赖性组蛋白 mRNA 的独特 3' 端是由一种独特的加工机制产生的，其中组蛋白 mRNA 前体在茎环下游被切割，但这种切割后不进行聚腺苷酸化。关键作用是由 U7 snRNP 发挥的，它是一种由约 60 个核苷酸的 U7 snRNA 和许多蛋白质组成的复合物。这些蛋白质中的一些，包括酶成分 CPSF73，与经典的切割和多聚腺苷酸化机制共享，这证明了这两种后生动物前 mRNA 3' 端加工机制具有共同的进化起源。对 U7 snRNP 的研究最终取得了突破，成功重建了一种完全重组的人类机制，该机制能够准确切割组蛋白前 mRNA，并确定其与预 mRNA 底物（含 13 种蛋白质和 2 种 RNA）复合物的结构，该底物准备进行切割反应。该结构揭示了 U7 snRNP 内出乎意料的相互作用网络以及激活催化休眠的 CPSF73 进行切割的惊人机制。这项工作为理解其他真核 3' 端加工机制提供了一个概念框架。
