February 8 2006
9:30 LSB 2320

Dr. Richard Gregory
The Wistar Institute, Philadelphia

The molecular machinery of RNAi: Insight into microRNA biogenesis and function


RNA interference (RNAi) describes the phenomenon whereby small non-coding RNA can silence gene expression. It is emerging that cells possess a wide repertoire of tiny regulatory RNAs that are critical for a variety of biological pathways and can repress genes via numerous mechanisms. For posttranscriptional gene silencing (PTGS), microRNAs (miRNAs), and small inhibitory RNAs (siRNAs), function as guide molecules inducing mRNA degradation or translational repression. My research focus has been dedicated to biochemically dissecting the pathways of how microRNAs (miRNAs) are generated, and how they exert their gene regulatory function in human cells. These studies have led to my identification of the ‘Microprocessor’ complex that is necessary and sufficient for processing long primary miRNA transcripts (pri-miRNAs) to hairpin-shaped precursor miRNA (pre-miRNA) intermediates. Additionally, isolation of a Dicer-containing complex revealed that processing of pre-miRNAs to the final ~22 nucleotide miRNA duplexes is physically and functionally coupled with assembly of an active RNA-induced silencing complex (RISC). Therefore, we propose that RISC is a trimeric protein complex comprising Dicer-TRBP-Argonaute2. Indeed, the functions of this purified complex fulfill all of the criteria that define RISC.