Structural visualization of RNA polymerase III transcription machineries

Yan Han,Susan Fishbain,Ivaylo Ivanov,Yuan He,Chunli Yan

doi:10.1038/s41421-018-0044-z

Yan Han, Susan Fishbain + Show 3 more

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https://doi.org/10.1038/s41421-018-0044-z

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Journal: Cell Discovery	Publication Date: Jul 31, 2018
Citations: 56	License type: open-access

Affiliation: Northwestern University, Georgia State University

Abstract

RNA polymerase III (Pol III) transcription initiation requires the action of the transcription factor IIIB (TFIIIB) and is highly regulated. Here, we determine the structures of Pol III pre-initiation complexes (PICs) using single particle cryo-electron microscopy (cryo-EM). We observe stable Pol III–TFIIIB complexes using nucleic acid scaffolds mimicking various functional states, in which TFIIIB tightly encircles the upstream promoter DNA. There is an intricate interaction between TFIIIB and Pol III, which stabilizes the winged-helix domains of the C34 subunit of Pol III over the active site cleft. The architecture of Pol III PIC more resembles that of the Pol II PIC than the Pol I PIC. In addition, we also obtain a 3D reconstruction of Pol III in complex with TFIIIB using the elongation complex (EC) scaffold, shedding light on the mechanism of facilitated recycling of Pol III prior to transcription re-initiation.

Highlights

In eukaryotes, at least three classes of RNA polymerases (Pol I–III) are required for the cellular RNA synthesis[1]
Local resolution estimation shows that the polymerase III (Pol III) core region is very rigid with resolution mostly at 3.9 Å, whereas peripheral regions such as the stalk and transcription factor IIIB (TFIIIB) are more mobile with a lower resolution (5–7 Å) (Supplementary Fig. S2c)
Our structures suggest a common architecture between Pol II and Pol III pre-initiation complexes (PICs), which is distinct from the Pol I PIC

Summary

Introduction

At least three classes of RNA polymerases (Pol I–III) are required for the cellular RNA synthesis[1]. RNA polymerase III (Pol III) transcribes various small stable RNAs that are essential in multiple cellular pathways, including pre-mRNA splicing (U6 snRNA) and protein synthesis (5S rRNA, tRNAs)[2]. While Brf[1] shows sequence homology to Rrn[7] and TFIIB, which are Pol I and II specific transcription factors, respectively[8], Bdp[1] is unique to Pol III9.

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