Structural analysis of human RPC32β-RPC62 complex

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• Transcription initiation by eukaryotic RNA polymerase (Pol) III depends on the RPC62/RPC39/RPC32 subcomplex.
• Two human RPC32 isoforms exist: RPC32α (restricted expression) and RPC32β (ubiquitous expression).

Purpose of the Study:

• To identify the RPC32 domain interacting with RPC62.
• To elucidate the structural basis of the RPC62-RPC32 interaction.
• To understand the role of RPC32 in RNA polymerase III assembly and function.

Main Methods:

• Protein complex crystallization and X-ray crystallography.
• Electron microscopy (EM) data analysis.
• Bioinformatic analysis of protein structures and interactions.

Main Results:

• A core-interacting domain of RPC32 was identified, mediating interaction with RPC62.
• The crystal structure revealed RPC32β binding to specific domains (winged helix 1 and 2, coiled coil) of RPC62.
• RPC32 acts as a molecular bridge, connecting different RPC62 domains.
• Structural data integrated with EM suggests a bi-functional role for RPC32 in Pol III assembly.

Conclusions:

• RPC32 is essential for bridging RPC62 domains, facilitating its integration into the Pol III holoenzyme.
• Subunit-specific interactions at the Pol III surface, mediated by factors like RPC32, are critical for holoenzyme function.
• Understanding the RPC62-RPC32 interaction provides insights into the regulation of transcription by RNA polymerase III.