ジャーナル: Cell / 年: 2017 タイトル: Cryo-EM Structure of a Pre-catalytic Human Spliceosome Primed for Activation. 著者: Karl Bertram / Dmitry E Agafonov / Olexandr Dybkov / David Haselbach / Majety N Leelaram / Cindy L Will / Henning Urlaub / Berthold Kastner / Reinhard Lührmann / Holger Stark / 要旨: Little is known about the spliceosome's structure before its extensive remodeling into a catalytically active complex. Here, we report a 3D cryo-EM structure of a pre-catalytic human spliceosomal B ...Little is known about the spliceosome's structure before its extensive remodeling into a catalytically active complex. Here, we report a 3D cryo-EM structure of a pre-catalytic human spliceosomal B complex. The U2 snRNP-containing head domain is connected to the B complex main body via three main bridges. U4/U6.U5 tri-snRNP proteins, which are located in the main body, undergo significant rearrangements during tri-snRNP integration into the B complex. These include formation of a partially closed Prp8 conformation that creates, together with Dim1, a 5' splice site (ss) binding pocket, displacement of Sad1, and rearrangement of Brr2 such that it contacts its U4/U6 substrate and is poised for the subsequent spliceosome activation step. The molecular organization of several B-specific proteins suggests that they are involved in negatively regulating Brr2, positioning the U6/5'ss helix, and stabilizing the B complex structure. Our results indicate significant differences between the early activation phase of human and yeast spliceosomes.