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Architecture of eukaryotic mRNA 3′-end processing machinery

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Science  24 Nov 2017:
Vol. 358, Issue 6366, pp. 1056-1059
DOI: 10.1126/science.aao6535

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Structural basis for mRNA 3′-end processing

The eukaryotic mRNA 3′-end processing machinery interacts with the transcription machinery and adds the polyadenylation tail on the mRNA substrate. Casañal et al. used cryo-electron microscopy, mass spectrometry, and biochemical reconstitutions to show that the mRNA 3′-end processing machinery is organized into nuclease, polymerase, and phosphatase modules. The polymerase module of the complex acts as a hub to bring the RNA substrate and the accessory factors together to achieve efficient and controlled polyadenylation coordinated with transcription.

Science, this issue p. 1056

Abstract

Newly transcribed eukaryotic precursor messenger RNAs (pre-mRNAs) are processed at their 3′ ends by the ~1-megadalton multiprotein cleavage and polyadenylation factor (CPF). CPF cleaves pre-mRNAs, adds a polyadenylate tail, and triggers transcription termination, but it is unclear how its various enzymes are coordinated and assembled. Here, we show that the nuclease, polymerase, and phosphatase activities of yeast CPF are organized into three modules. Using electron cryomicroscopy, we determined a 3.5-angstrom-resolution structure of the ~200-kilodalton polymerase module. This revealed four β propellers, in an assembly markedly similar to those of other protein complexes that bind nucleic acid. Combined with in vitro reconstitution experiments, our data show that the polymerase module brings together factors required for specific and efficient polyadenylation, to help coordinate mRNA 3′-end processing.

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