Question

At what step of miRNA/siRNA processing is RISC involved? What is the difference between RISC and RISC*? How does RISC* catalyze mRNA inhibition? How does RdRP amplify gene silencing?

Answer 1

RISC is involved in miRNA/siRNA processing after DICER cleavage. RISC* is the active form that catalyzes mRNA inhibition, and RdRP amplifies gene silencing by creating more siRNAs.

Step-by-step explanation:

The RNA-induced silencing complex (RISC) becomes involved in miRNA/siRNA processing after the generation of mature miRNAs or siRNAs by DICER. RISC uses these RNA molecules to target and silence corresponding mRNAs, with miRNA-RISC leading to the degradation or translational inhibition of the target mRNA based on the degree of complementarity.

RISC and RISC* differ in their states; RISC* is the activated form of RISC, containing a single-stranded RNA ready to bind to its target mRNA. This active complex catalyzes mRNA inhibition by either inducing cleavage or repressing translation, depending on the match between the RNA in RISC* and the target mRNA. The more complementary it is to the target, the more likely it is for the mRNA to be cleaved.

RdRP (RNA-dependent RNA polymerase) amplifies gene silencing by using siRNAs as templates to create more siRNA molecules. These new siRNAs can form additional RISC complexes, leading to a larger amount of mRNA being targeted and silenced.