TRBP alters human precursor microRNA processing in vitro

Substrate-specific structural rearrangements of human Dicer

Dicer plays a central role in RNA interference pathways by cleaving double-stranded RNAs (dsRNAs) to produce small regulatory RNAs. Human Dicer can process long double-stranded and hairpin precursor RNAs to yield short interfering RNAs (siRNAs) or microRNAs (miRNAs), respectively. Previous studies have shown that pre-miRNAs are cleaved more rapidly than pre-siRNAs in vitro and are the predominant natural Dicer substrates. We have used electron microscopy and single particle analysis of Dicer–RNA complexes to gain insight into the structural basis for human Dicer’s substrate preference. Our studies show that Dicer traps pre-siRNAs in a non-productive conformation, while interactions of Dicer with pre-miRNAs and dsRNA binding proteins induce structural changes in the enzyme that enable productive substrate recognition in the central catalytic channel. These findings implicate RNA structure and cofactors in determining substrate recognition and processing efficiency by human Dicer.

Molecular mechanisms of RNA interference

Small RNA molecules regulate eukaryotic gene expression during development and in response to stresses including viral infection. Specialized ribonucleases and RNA-binding proteins govern the production and action of small regulatory RNAs. After initial processing in the nucleus by Drosha, precursor microRNAs (pre-miRNAs) are transported to the cytoplasm, where Dicer cleavage generates mature microRNAs (miRNAs) and short interfering RNAs (siRNAs). These double-stranded products assemble with Argonaute proteins such that one strand is preferentially selected and used to guide sequence-specific silencing of complementary target mRNAs by endonucleolytic cleavage or translational repression. Molecular structures of Dicer and Argonaute proteins, and of RNA-bound complexes, have offered exciting insights into the mechanisms operating at the heart of RNA-silencing pathways.

Dicer partners expand the repertoire of miRNA targets

Processing of pre-miRNAs by Dicer is regulated by its dsRNA-binding protein partner, and leads to the generation of alternative miRNA forms with distinct target sets.