A Hub for 3'-end Processing: Structural Insights into mRNA Polyadenylation
by Dr. Ana Casañal (MRC-Laboratory of Molecular Biology, Passmore Lab, Cambridge, UK)
at ALBA Synchrotron ( Marie Curie Briefing Room )
Almost all eukaryotic pre-mRNAs must undergo 5′ capping, splicing and 3′-end processing before they can be transported to the cytoplasm for their translation into proteins. 3′-end processing involves over 20 different protein factors that also co-ordinate transcription termination. The cleavage and polyadenylation factor (CPF) is an essential component of the 3′-end machinery that cleaves pre-mRNA transcripts and adds the 3’ polyA tails. Despite its fundamental importance, we are still far from understanding the molecular mechanisms of CPF. Here, we identify a sub-complex of the yeast CPF, the polyadenylation module (pAm), which acts as a hub for protein-protein interactions. Using cryo-EM we determine a 3.5 Å structure of the Cft1-Pfs2-Yth1 subunits of pAm. This consists of 4 beta propellers in Cft1 and Pfs2 that are strikingly similar to other interaction hubs involved in DNA and RNA processing. The zinc finger Yth1 protein extends from the side, providing an RNA binding surface. Biochemical studies confirm the structural observations and indicate the important role of pAm as the scaffold element of CPF to assemble other CPF subunits, including the poly(A) polymerase, and accessory factors of the 3’end processing machinery on RNA.
Architecture of Eukaryotic mRNA 3’-end Processing Machinery
Casañal A., Kumar A., Hill C. H., Easter A.D., Emsley P., Degliesposti G., Gordiyenko Y., Santhanam B., Wolf J., Wiederhold K., Dornan G. L., Skehel M., Robinson C. V., Passmore L. A. Science (2017). doi: 10.1126/science.aao6535.