TY - JOUR T1 - Negative Cooperativity between Gemin2 and RNA Determines RNA Selection and Release of the SMN Complex in snRNP Assembly JF - bioRxiv DO - 10.1101/312124 SP - 312124 AU - Hongfei Yi AU - Li Mu AU - Congcong Shen AU - Xi Kong AU - Yingzhi Wang AU - Yan Hou AU - Rundong Zhang Y1 - 2018/01/01 UR - http://biorxiv.org/content/early/2018/05/02/312124.abstract N2 - The assembly of snRNP cores, in which seven Sm proteins, D1/D2/F/E/G/D3/B, form a ring around snRNAs, is the early step of spliceosome formation and essential to eukaryotes. It is mediated by the PMRT5 and SMN complexes sequentially in vivo. The deficiency of SMN causes neurodegenerative disease spinal muscular atrophy (SMA). How the SMN complex assembles snRNP cores in the second phase is largely unknown, especially how the SMN complex achieves stringent RNA specificity, ensuring seven Sm proteins assemble only around snRNAs, by requiring an extra 3’-adjacent stem-loop (SL) in addition to a nonameric Sm site RNA (PuAUUUNUGPu) on which snRNP cores can spontaneously form without chaperons in vitro. Moreover, how the SMN complex is released from snRNP cores is unknown. Here we show that Gemin2 of the SMN complex and RNA allosterically and mutually inhibit each other’s binding to SmD 1/D2/F/E/G, coupling RNA selection with the SMN complex’s release. Using crystallographic and biochemical approaches, we found that Gemin2 constrains the horseshoe-shaped SmD1/D2/F/E/G in a physiologically relevant, narrow state, which prefers the snRNP-code (both the Sm site and 3’-SL)-containing RNA for assembly. Moreover, the assembly of RNA widens SmD1/D2/F/E/G, causes Gemin2’s release allosterically and allows SmD3/B to join. By structural analysis we further propose a structural mechanism for the allosteric conformational changes. These findings provide deeper insights into the SMN complex’s mode of action and snRNP assembly, and facilitate potential therapeutic studies of SMA. ER -