Didychuk Allison L, Montemayor Eric J, Carrocci Tucker J, DeLaitsch Andrew T, Lucarelli Stefani E, Westler William M, Brow David A, Hoskins Aaron A, Butcher Samuel E
Department of Biochemistry, University of Wisconsin, Madison, Wisconsin, 53706, USA.
Department of Biomolecular Chemistry, University of Wisconsin, Madison, Wisconsin, 53706, USA.
Nat Commun. 2017 Sep 8;8(1):497. doi: 10.1038/s41467-017-00484-w.
U6 small nuclear ribonucleoprotein (snRNP) biogenesis is essential for spliceosome assembly, but not well understood. Here, we report structures of the U6 RNA processing enzyme Usb1 from yeast and a substrate analog bound complex from humans. Unlike the human ortholog, we show that yeast Usb1 has cyclic phosphodiesterase activity that leaves a terminal 3' phosphate which prevents overprocessing. Usb1 processing of U6 RNA dramatically alters its affinity for cognate RNA-binding proteins. We reconstitute the post-transcriptional assembly of yeast U6 snRNP in vitro, which occurs through a complex series of handoffs involving 10 proteins (Lhp1, Prp24, Usb1 and Lsm2-8) and anti-cooperative interactions between Prp24 and Lhp1. We propose a model for U6 snRNP assembly that explains how evolutionarily divergent and seemingly antagonistic proteins cooperate to protect and chaperone the nascent snRNA during its journey to the spliceosome.The mechanism of U6 small nuclear ribonucleoprotein (snRNP) biogenesis is not well understood. Here the authors characterize the enzymatic activities and structures of yeast and human U6 RNA processing enzyme Usb1, reconstitute post-transcriptional assembly of yeast U6 snRNP in vitro, and propose a model for U6 snRNP assembly.
U6小核核糖核蛋白（snRNP）的生物合成对于剪接体组装至关重要，但目前尚未完全了解。在此，我们报道了来自酵母的U6 RNA加工酶Usb1以及来自人类的与底物类似物结合的复合物的结构。与人类直系同源物不同，我们发现酵母Usb1具有环磷酸二酯酶活性，会留下一个末端3'磷酸基团，从而防止过度加工。Usb1对U6 RNA的加工会显著改变其对同源RNA结合蛋白的亲和力。我们在体外重建了酵母U6 snRNP的转录后组装过程，该过程通过一系列复杂的交接进行，涉及10种蛋白质（Lhp1、Prp24、Usb1和Lsm2 - 8）以及Prp24和Lhp1之间的反协同相互作用。我们提出了一个U6 snRNP组装模型，该模型解释了在进化上不同且看似拮抗的蛋白质如何在新生snRNA前往剪接体的过程中协同作用以保护和陪伴它。U6小核核糖核蛋白（snRNP）生物合成的机制尚未完全了解。在此，作者表征了酵母和人类U6 RNA加工酶Usb1的酶活性和结构；在体外重建了酵母U6 snRNP的转录后组装过程；并提出了一个U6 snRNP组装模型。
