The structural landscape of Microprocessor-mediated processing of pri-let-7 miRNAs

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• MicroRNA (miRNA) biogenesis is crucial for gene regulation.
• The Microprocessor (MP) complex, comprising Drosha and DGCR8, initiates miRNA production by cleaving pri-miRNA hairpins.
• Sequence motifs within pri-miRNAs influence MP recognition and processing efficiency.

Purpose of the Study:

• To elucidate the structural basis of Microprocessor complex recognition and cleavage of diverse pri-miRNAs.
• To characterize the role of specific sequence motifs, such as the 'flipped U with paired N' (fUN) motif, in pri-miRNA processing.
• To investigate the contribution of SRSF3 to Microprocessor fidelity.

Main Methods:

• Cryoelectron microscopy (cryo-EM) of human Microprocessor complex bound to let-7 family pri-miRNAs.
• Biochemical assays to study MP-pri-miRNA interactions and cleavage dynamics.
• Structural analysis of MP-SRSF3-pri-let-7f1 complex.

Main Results:

• Demonstrated the structural plasticity of the Microprocessor complex in accommodating various pri-miRNAs.
• Identified the 'flipped U with paired N' (fUN) motif as a key feature for MP recognition.
• Explained the generation of non-canonical precursors from class-II pri-let-7 members.
• Revealed how SRSF3 enhances MP fidelity through interactions with the CNNC motif and Drosha's PAZ-like domain.

Conclusions:

• The Microprocessor complex exhibits flexible recognition mechanisms for diverse pri-miRNAs.
• Specific sequence motifs and accessory factors like SRSF3 are critical for accurate and regulated miRNA processing.
• Structural insights provide a deeper understanding of the molecular basis of miRNA biogenesis.