Question

5. How is RNA interference (RNAI) used to regulate gene expression in eukaryotes? 5 pts

Answer 1

RNAi is used to regulate gene expression in Eukaryotes by two main pathways:

• microRNA mediated:
  microRNA mediated RNAi involves the use of non-coding microRNA species. Fully mature microRNA (miRNA) species are RNA molecules that are post-transcriptionally modified into stem-loop structures capable of binding to the 3' UTRs of several, related mRNA species. A mature miRNA molecule can bind to the 3'UTRs of mRNA molecules, and either inhibit the biding of factors that promote translation or actively promote the degradation of the mRNA. A single miRNA species can affect the translation levels of many different proteins (on the order of 10²).
• small interfering RNA mediated:
  Small Interfering RNA (siRNA) species are 20-24 bp, double-stranded RNA molecules that, along with the RNA-induced Silencing Complex (RISC), specifically target mRNA species for degradation. siRNA molecules have sequences complementary to the target mRNA, as opposed to miRNAs which do not have strict complementarity with their target sequences. The RISC-siRNA scans mRNA molecules for a target by scanning mRNA molecules it encounters. Once targets are identified, the target mRNA molecule degraded by associate factors.

The concerted action of miRNA and siRNA species allows for RNAi to regulate eukaryotic gene expression.