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Unformatted text preview: observation: double-stranded RNA molecules are much more
potent inhibitors of gene expression. RNA interference
molecules are cleaved by Dicer
The resulting small interfering
The antisense strand of the
siRNA is bound by RISC (RNAinduced silencing complex) RNA interference
RISC interacts with the target
message, resulting in another
Which is cleaved by Dicer...etc.
dsRNA is a catalyst for the
destruction of all mRNA for that
gene RNA interference RNAi happens in nearly all cell types, in all eukaryotes tested to date.
Why might this have evolved? MicroRNAs (miRNAs)
Similar to siRNAs, miRNAs are small RNA molecules that form a RISC
to target the expression of a particular gene
Unlike siRNAs, miRNAs are usually encoded by a cellular gene and
probably function as a form of gene regulation
Unlike siRNAs, miRNAs prevent translation (rather than lead to
mRNA degradation) Feature siRNA miRNA Origin mRNA, virus, or transposon Distinct miRNA gene Cleavage of RNA duplex or ssRNA
hairpins ssRNA that forms short ds
hairpins Size 21-25 nucleotides 21-25 nucleotides Primary Action Degradation of mRNA Inhibition of translation Target Genes from which they were Genes other than those from
which they were transcribed Protei...
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