Structure of the TFIIIC subcomplex \u03c4A provides insights into RNA polymerase III pre-initiation complex formation

Matthias K Vorländer,Helga Grötsch,Anna Jungblut,Florence Baudin,Christoph W Müller,Kai Karius,Jan Kosinski

doi:10.1038/s41467-020-18707-y

Abstract

Transcription factor (TF) IIIC is a conserved eukaryotic six-subunit protein complex with dual function. It serves as a general TF for most RNA polymerase (Pol) III genes by recruiting TFIIIB, but it is also involved in chromatin organization and regulation of Pol II genes through interaction with CTCF and condensin II. Here, we report the structure of the S. cerevisiae TFIIIC subcomplex τA, which contains the most conserved subunits of TFIIIC and is responsible for recruitment of TFIIIB and transcription start site (TSS) selection at Pol III genes. We show that τA binding to its promoter is auto-inhibited by a disordered acidic tail of subunit τ95. We further provide a negative-stain reconstruction of τA bound to the TFIIIB subunits Brf1 and TBP. This shows that a ruler element in τA achieves positioning of TFIIIB upstream of the TSS, and suggests remodeling of the complex during assembly of TFIIIB by TFIIIC.

Highlights

Transcription factor (TF) IIIC is a conserved eukaryotic six-subunit protein complex with dual function
We propose a model how a ruler element in τA positions Brf[1] and TATA-box-binding protein (TBP) upstream of the transcription start site (TSS), where TFIIIB can assemble on a suitable DNA sequence by using a proofreading mechanism that contributes to TSS selection fidelity
We report structural models for S. cerevisiae τA alone, and for τA bound to the TFIIIB subunits Brf[1] and TBP in absence of DNA, which provide insights into yeast-specific and general features of τA

Summary

Introduction

Transcription factor (TF) IIIC is a conserved eukaryotic six-subunit protein complex with dual function It serves as a general TF for most RNA polymerase (Pol) III genes by recruiting TFIIIB, but it is involved in chromatin organization and regulation of Pol II genes through interaction with CTCF and condensin II. We report the structure of the S. cerevisiae TFIIIC subcomplex τA, which contains the most conserved subunits of TFIIIC and is responsible for recruitment of TFIIIB and transcription start site (TSS) selection at Pol III genes. TFIIIB consists of subunits B-related factor 1 (Brf1), TATA-box-binding protein (TBP) and B double prime 1 (Bdp1), which together encircle the upstream promoter DNA in the pre-initiation complex and allosterically activate melting of the DNA double helix[2,3]. The structure of a τ60–τ91 heterodimer is available[19], as well as a winged-helix (WH) domain of τ138 (ref. 9)

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