Dicer-TRBP complex formation ensures accurate mammalian microRNA biogenesis

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• RNA-mediated gene silencing relies on microRNAs (miRNAs) processed by the endonuclease Dicer.
• RNA-binding proteins TRBP and PACT are known to influence miRNA biogenesis but their precise interaction with Dicer and genome-wide impact remain unclear.

Purpose of the Study:

• To elucidate the structural basis of the Dicer-TRBP interaction.
• To investigate the functional consequences of TRBP/PACT binding on Dicer activity and miRNA processing.
• To determine the genome-wide effects of Dicer-associated proteins on miRNA generation and gene silencing.

Main Methods:

• X-ray crystallography to determine the structure of the human Dicer-TRBP interface.
• Biochemical assays to analyze Dicer-TRBP/PACT binding and mutual exclusion.
• Engineering a catalytically active Dicer mutant unable to bind TRBP/PACT.
• Introduction of the engineered Dicer into Dicer-deficient mammalian cells to assess miRNA processing defects.

Main Results:

• The crystal structure revealed the specific interface residues mediating Dicer-TRBP binding.
• Conserved residues between TRBP and PACT indicate similar binding modes and mutual exclusion from Dicer.
• An engineered Dicer mutant lacking TRBP/PACT binding showed selective defects in guide strand selection during miRNA processing.
• These findings highlight the role of Dicer-associated proteins in ensuring accurate miRNA biogenesis.

Conclusions:

• TRBP and PACT bind Dicer through a conserved interface, influencing its function.
• Dicer-associated proteins are critical for the fidelity of miRNA processing and subsequent gene silencing.
• Understanding these interactions provides insights into maintaining gene silencing accuracy.