Structure of human RNA polymerase III

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• RNA Polymerase (Pol) III transcribes essential small RNAs, impacting cellular growth and lifespan.
• Pol III dysregulation is implicated in cancer, neurodevelopmental disorders, and altered viral responses.

Purpose of the Study:

• To determine the high-resolution structure of human Pol III using cryo-electron microscopy (cryo-EM).
• To map and rationalize the effects of known genetic mutations on Pol III function and stability.
• To elucidate the structure and function of the RPC5 C-terminal extension in higher eukaryotes.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for overall structure determination.
• X-ray crystallography and Small-Angle X-ray Scattering (SAXS) for detailed domain analysis.
• Cellular assays to assess the functional role of the RPC5 module in vivo.

Main Results:

• A 4.0 Å cryo-EM reconstruction of human Pol III was achieved, enabling precise localization of disease-associated mutations.
• Mutations linked to neurodevelopmental defects cluster in regions critical for Pol III stability and biogenesis.
• Mutations affecting viral sensing are positioned near DNA-binding sites, suggesting impaired cytosolic viral DNA detection.
• The structure of the RPC5 C-terminal extension was resolved, revealing its role in Pol III assembly and stability.

Conclusions:

• The structural insights rationalize the molecular basis of Pol III-related disorders.
• The findings highlight distinct functional roles for different mutation sites within Pol III.
• The RPC5 C-terminal extension is identified as a key factor in human Pol III integrity and function.