Modeling miRNA mechanisms Two more key players in the microRNA regulatory system have been
identified By Cathy Holding
Small, noncoding RNA molecules mediate a posttranscriptional gene-silencing mechanism that regulates
the expression of developmental genes by inhibiting the translation of target mRNAs. This mechanism
is common to plants, fungi, and animals, and the generation of these microRNAs (miRNAs, also known
as small inhibitory RNAs or siRNAs) involves a series of sequential steps, where primary RNA
transcripts (pri-miRNAs) are cleaved in the nucleus to smaller pre-miRNAs. These are transported to
the cytosol where Dicer, a member of the RNAse III nuclease family, further processes them to yield
mature miRNAs. MiRNAs associate with multicomponent ribonucleoprotein complexes, or RISCs, which
effect the silencing of the target mRNA molecules. Two papers in the September 25 Nature report
previously unidentified key components in the miRNA regulatory system. Yountae Lee and colleagues at
Seoul National University identify a protein that cleaves pri-miRNAs to pre-miRNAs, while Amy Caudy
and colleagues at Cold Spring Harbor Laboratory identify another component of the RISC complex.
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Kind Regards, Robert Karl Stonjek.