Structural insights into transcriptional regulation of human RNA polymerase III

RNA polymerase III (Pol III) synthesizes structured, essential small RNAs, such as transfer RNA, 5S ribosomal RNA and U6 small nuclear RNA. Pol III, the largest nuclear RNA polymerase, is composed of a conserved core region and eight constitutive regulatory subunits, but how these factors jointly regulate Pol III transcription remains unclear. Here, we present cryo-EM structures of human Pol III in both apo and elongating states, which unveil both an orchestrated movement during the apo-to-elongating transition and an unexpected apo state in which the RPC7 subunit tail occupies the DNA-RNA-binding cleft of Pol III, suggesting that RPC7 plays important roles in both autoinhibition and transcription initiation. The structures also reveal a proofreading mechanism for the TFIIS-like subunit RPC10, which stably retains its catalytic position in the secondary channel, explaining the high fidelity of Pol III transcription. Our work provides an integrated picture of the mechanism of Pol III transcription regulation. High-resolution cryo-EM structures of human RNA Pol III in both apo and elongating states provide insights into an autoinhibitory mechanism controlling the transition to transcription elongation unique to the mammalian holoenzyme.

Automated summary

The study provides insights into the structure of human Pol III in different states, highlighting the important roles of RPC7 and RPC10 subunits in Pol III transcription, and offers a comprehensive understanding of the regulation mechanism of Pol III transcription.