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RNAi Glossary

  • Argonaute - A family of proteins containing multiple domains and involved in RNA interference (RNAi). Argonatue is the main component of RNAi effector complex, the so called siRNA induced silencing complex (RISC) and aids in target recognition and cleavage during RNAi.
  • 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.
  • MicroRNA (miRNA) - 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-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 - 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.
  • 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.
  • shRNA - shRNA or short hairpin RNA is an RNA molecule that contains a fragment of a sense strand and an antisense strand, and a short loop sequence between the sense and antisense fragment. Due to the complementarity of the sense and antisense fragments in their sequence, such RNA molecules tend to form hairpin-shaped double-stranded RNA (dsRNA) by flipping back on the loop sequence. Usually, shRNA is cloned into a vector so that once the vector is introduced into a cell, the shRNA can be transcribed by a pol III type promoter in the vector. The expressed shRNA is then exported into the cytoplasm where it is processed by dicer into siRNA which then triggers RNAi.
  • Small Interfering RNA (siRNA) - Small Interfering RNA (siRNA) is 21~23-nt double-stranded RNA molecules. It guides the cleavage and degradation of its cognate RNA.

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