Lower and upper stem-single-stranded RNA junctions together determine the Drosha cleavage site

Area of Science:

• Molecular Biology
• RNA Biology
• Biochemistry

Background:

• MicroRNA (miRNA) biogenesis is crucial for gene regulation.
• The Drosha-DGCR8 complex initiates miRNA biogenesis by processing primary miRNA (pri-miRNA).
• The precise mechanism determining the Drosha cleavage site remained unclear.

Purpose of the Study:

• To elucidate how the Drosha-DGCR8 complex determines the cleavage site on pri-miRNA.
• To investigate the role of stem-ssRNA junction distances in Drosha processing.
• To understand the mechanism generating 5' isomiRs.

Main Methods:

• Utilized miRNA-offset RNAs to map Drosha cleavage sites.
• Experimentation conducted in human cells.
• Analysis of Drosha processing precision based on stem-ssRNA junction distances.

Main Results:

• The Drosha-DGCR8 complex measures distances from both lower and upper stem-single-stranded RNA (ssRNA) junctions.
• Optimal distances from both junctions are critical for precise Drosha processing.
• Non-optimal distances result in multiple cleavage sites, generating 5' isomiRs.

Conclusions:

• The Microprocessor complex employs a dual-distance measurement mechanism for pri-miRNA cleavage site determination.
• This mechanism ensures precise miRNA processing.
• Imprecise distance measurements by Drosha-DGCR8 lead to the generation of 5' isomiRs, revealing a novel mechanism.