Structure of human RNA polymerase III elongation complex

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• RNA polymerase III (Pol III) transcribes vital small RNAs, and its dysregulation is linked to human diseases like cancer.
• Human Pol III exists in two isoforms (Pol IIIα and Pol IIIβ), differing only in the RPC7 subunit, but its structure remains unelucidated.
• Understanding human Pol III structure is crucial for deciphering its role in health and disease.

Purpose of the Study:

• To determine the high-resolution structures of the 17-subunit human Pol IIIα complex.
• To elucidate the structural differences between yeast and human Pol III.
• To investigate the molecular mechanisms underlying human Pol III transcriptional regulation and its connection to cancer.

Main Methods:

• Cryo-electron microscopy (Cryo-EM) to resolve the structures of human Pol IIIα.
• Comparative structural analysis with yeast Pol III.
• Biochemical assays to study subunit interactions and regulatory mechanisms.

Main Results:

• The structure of human Pol IIIα was determined in both backtracked and post-translocation states.
• Human Pol III shares a conserved catalytic core with yeast Pol III but possesses unique subunits: RPC3-RPC6-RPC7 heterotrimer and RPC10.
• Detailed interactions of RPC10, RPC7, RPC6, and their roles in stabilizing the complex and potential regulation by Maf1 were revealed.

Conclusions:

• The solved structures provide unprecedented insights into the human Pol IIIα complex.
• Specific structural features, like the RPC7α N-terminal region and RPC6 FeS cluster, are key to human Pol III regulation.
• Findings explain the increased Pol III activity observed in RPC7α-dominant cancer cells, opening avenues for therapeutic strategies.