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Structural basis of RNA polymerase III transcription repression by Maf1

By Matthias K. Vorländer, Florence Baudin, Robyn D. Moir, René Wetzel, Wim J. H. Hagen, Ian M Willis, Christoph W Müller

Posted 29 Nov 2019
bioRxiv DOI: 10.1101/859132 (published DOI: 10.1038/s41594-020-0383-y)

Maf1 is a highly conserved central regulator of transcription by RNA polymerase III (Pol III), and Maf1 activity influences a wide range of phenotypes from metabolic efficiency to lifespan. Here, we present a 3.3 Å cryo-EM structure of yeast Maf1 bound to Pol III, which establishes how Maf1 achieves transcription repression. In the Maf1-bound state, Pol III elements that are involved in transcription initiation are sequestered, and the active site is sealed off due to ordering of the mobile C34 winged helix 2 domain. Specifically, the Maf1 binding site overlaps with the binding site of the Pol III transcription factor TFIIIB and DNA in the pre-initiation complex, rationalizing that binding of Maf1 and TFIIIB to Pol III are mutually exclusive. We validate our structure using variants of Maf1 with impaired transcription-inhibition activity. These results reveal the exact mechanism of Pol III inhibition by Maf1, and rationalize previous biochemical data.

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