Structural basis of RNA conformational switching in the transcriptional regulator 7SK RNP

Area of Science:

• Structural Biology
• Molecular Biology
• Virology

Background:

• 7SK non-coding RNA (7SK) is a key negative regulator of RNA polymerase II (RNA Pol II) elongation.
• The 7SK ribonucleoprotein complex (RNP) is essential for regulating transcription and is exploited by HIV-1.
• Methylphosphate capping enzyme (MePCE) and La-related protein 7 (Larp7) form a stable core with 7SK RNA.

Purpose of the Study:

• To elucidate the structural mechanisms of the 7SK core RNP.
• To understand the roles of MePCE and Larp7 in 7SK RNP assembly and regulation.
• To reveal how the 7SK RNP controls RNA polymerase II (RNA Pol II) and P-TEFb activity.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine the structures of the 7SK core RNP.
• Nuclear Magnetic Resonance (NMR) spectroscopy.
• Biochemical assays and cellular studies.

Main Results:

• Determined cryo-EM structures of 7SK core RNP in circular and linear conformations.
• Uncovered a common RNA-dependent MePCE-Larp7 complex structure.
• Revealed MePCE catalytic inactivation, Larp7's chaperone role via RNA interactions, and the RNP's scaffold function for conformational switching.

Conclusions:

• The 7SK core RNP structure provides insights into the regulation of transcription elongation.
• Larp7 acts as an RNP chaperone, facilitating dynamic conformational changes in the 7SK RNP.
• The MePCE-7SK-Larp7 complex is a scaffold essential for P-TEFb sequestration and release, impacting viral replication.