RNAi Glossary

• Dicer - Dicer is a member of the RNase III family of nucleases that specifically cleave double-stranded RNAs. Dicer processes long dsRNA into siRNA of 21-23 nt.

• Interferon - A small and highly potent molecule that functions in an autocrine and paracrine manner, and that induces cells to resist viral replication. This term is related to RNAi because in mammals introduction of dsRNA longer than 30 nt induces a sequence-nonspecific interferon response.

• Micro-RNA - Micro-RNAs (miRNA) are single-stranded RNAs of 22-nt that are processed from ~70-nt hairpin RNA precursors by Rnase III nuclease Dicer. Similar to siRNAs, miRNAs can silence gene activity via destruction of homologous mRNA in plants or blocking its translation in plants and animals.

• Post-Transcriptional Gene Silencing - Post-transcriptional gene silencing (PTGS) is a sequence-specific RNA degradation system designed to act as an anti-viral defense mechanism. A form of PTGS triggered by transgenic DNA, called co-suppression, was initially described in plants and a related phenomenon, termed quelling, was later observed in the filamentous fungus Neurospora crassa

• Ribozyme - Ribozymes are RNA molecules that act as enzymes in the absence of proteins.

• RNA Interference - RNA Interference (RNAi), a term coined by Fire et al in 1998, is a phenomenon that small double-stranded RNA (referred as small interference RNA or siRNA) can induce efficient sequence-specific silence of gene expression.

• RNA-Directed DNA Methylation - RNA-directed DNA methylation (RdDM) is an RNA directed silencing mechanism found in plants. Similar to RNA interference (RNAi), RdDM requires a double-strand RNA that is cut into short 21-26-nt fragments. DNA sequences homologous to these short RNAs are then methylated and silenced.

• RNA-Induced Silencing Complex - RNA-induced silencing complex (RISC) is an siRNA-directed endonuclease, catalyzing cleavage of a single phosphodiester bond on the RNA target.

• RNAi Trigger - RNAi triggers are double-stranded RNAs containing 21-23 nt sense and antisens strands hybridized to have 2 nt overhangs at both 3' ends.

• Small Interfering RNA - Small Interfering RNA (siRNA) is 21-23-nt double-strand RNA. It guides the cleavage and degradation of its cognate RNA.