Structural basis of microRNA processing by Dicer-like 1.

Area of Science:

• Molecular Biology
• Plant Science
• Biochemistry

Background:

• MicroRNAs (miRNAs) regulate gene expression by targeting messenger RNAs (mRNAs).
• In animals, miRNA precursors are processed by Drosha and Dicer enzymes.
• Plants utilize a single enzyme, Dicer-like 1 (DCL1), for both processing steps, a mechanism not fully understood.

Purpose of the Study:

• To elucidate the structural basis of how Arabidopsis Dicer-like 1 (DCL1) recognizes and processes both pri-miRNA and pre-miRNA substrates.
• To understand the sequential cleavage mechanism employed by DCL1 in plant miRNA biogenesis.

Main Methods:

• Single-particle cryo-electron microscopy (cryo-EM) was used to determine the structures of Arabidopsis DCL1.
• Structures were obtained for DCL1 complexed with both pri-miRNA and pre-miRNA substrates in cleavage-competent states.

Main Results:

• The cryo-EM structures reveal the plasticity of the PAZ domain, crucial for binding both pri-miRNA and pre-miRNA.
• The helicase module of DCL1 appears to function as a motor, facilitating substrate transfer between sequential cleavage events.
• The structures provide atomic-level insights into the distinct substrate recognition and processing steps.

Conclusions:

• The study uncovers the structural mechanisms underlying DCL1's dual cleavage function in plant miRNA biogenesis.
• The findings highlight the critical role of PAZ domain plasticity and the helicase module in DCL1 activity.
• This work provides a foundation for understanding plant miRNA processing regulation and offers insights into Dicer enzyme function across species.