WD40 domain hooks pre-snRNAs
- Chao Xu Ph.D at school of Life Sciences, USTC, uncovered the molecular mechanism of the recognition of pre-snRNAs by the Gemin5 WD40 domain.This project was collaborated with professor Jinrong Min (University of Toronto) and was published as an advance online paper on Genes & Development（Genes & Development 2016, doi:10.1101/gad.291377.116）.
In cytoplasm, the survival of motor neuron (SMN) complex delivers pre-small nuclear RNAs (pre-snRNAs) to the heptameric Sm ring for the assembly of the ring complex on pre-snRNAs at the conserved Sm site [A(U)4–6G].Gemin5, a WD40 protein component of the SMN complex, is responsible for recognizing pre-snRNAs. In addition,Gemin5 has been reported to specifically bind to the m7G cap. In this study, we show that the WD40 domain ofGemin5 is both necessary and sufficient for binding the Sm site of pre-snRNAs by isothermal titration calorimetry(ITC) and mutagenesis assays. We further determined the crystal structures of the WD40 domain of Gemin5 incomplex with the Sm site orm7G cap of pre-snRNA, which reveal that the WD40 domain of Gemin5 recognizes theSm site and m7G cap of pre-snRNAs via two distinct binding sites by respective base-specific interactions. In addition,we also uncovered a novel role of Gemin5 in escorting the truncated forms of U1 pre-snRNAs for properdisposal. Overall, the elucidated Gemin5 structures will contribute to a better understanding of Gemin5 in smallnuclear ribonucleic protein (snRNP) biogenesis as well as, potentially, other cellular activities.