Gene silencing triggers in the form of double stranded RNA may be presented in the cell as synthetic RNAs or replicating viruses, or may be transcribed from nuclear genes. These are recognized and processed into small interfering RNAs by Dicer. The duplex siRNAs are passed to RISC (RNA-induced silencing complex), and the complex becomes activated by unwinding of the duplex. Activated RISC complexes can regulate gene expression at many levels. Almost certainly, such complexes act by promoting RNA degradation and translational inhibition. However, similar complexes probably also target chromatin remodeling. Amplification of the silencing signal in plants may be accomplished by siRNAs priming RNA-directed RNA polymerase (RdRP)-dependent synthesis of new dsRNA. This could be accomplished by RISC-mediated delivery of an RdRP or by incorporation of the siRNA into a distinct, RdRP-containing complex.
This image is linked to the following Scitable pages:
While we've been taught: don't shoot the messenger, our cells haven’t gotten the message. See how small bits of non-coding RNA target mRNA for destruction and regulate gene expression.
Transcriptionally inactive heterochromatin is vital to sustaining stable chromosome structure throughout the cell cycle. See how heterochromatin formation depends on RNA interference.
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