Short RNA duplexes guide sequence-dependent cleavage by human Dicer.

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Dicer is a ribonuclease III enzyme essential for RNA processing and degradation.
• Dicer possesses a double-stranded RNA (dsRNA) binding domain and cleaves dsRNA.
• Understanding Dicer's substrate selectivity is key to elucidating its role in gene regulation.

Purpose of the Study:

• To investigate the substrate selectivity of Dicer enzyme.
• To determine the structural features of RNA duplexes that Dicer recognizes for cleavage.
• To explore the potential for pre-microRNAs (pre-miRNAs) to act as bipartite substrates.

Main Methods:

• Utilized bipartite RNA substrates to examine Dicer binding and cleavage.
• Performed chemical modifications on RNA substrates to probe the role of specific chemical groups.
• Analyzed the structure of natural pre-miRNAs and their potential interactions with mRNA.

Main Results:

• Dicer binds and cleaves RNA duplexes with a 2-nucleotide 3 -overhang at a fixed distance.
• The ribose 2 -hydroxyl group is not essential for Dicer binding, but is important for cleavage near the scissile bonds.
• Dicer exhibits flexible substrate selectivity based on the overall helical shape of the RNA.
• Natural pre-miRNAs can form substrate mimics with complementary mRNA sequences, inducing Dicer cleavage.

Conclusions:

• Dicer's substrate recognition involves a flexible mechanism focusing on the RNA helix's shape.
• Pre-miRNAs may utilize this mechanism to engage in seed-independent Dicer-mediated cleavage.
• This finding has implications for understanding microRNA biogenesis and function.