RNAi: Regulating Gene Expression by RNA

RNA interference (RNAi) has emerged as one of the significant mechanisms playing a major role in gene expression regulation. The mechanism relies on diverse small noncoding RNAs, the prominent being siRNAs (small interfering RNAs) and miRNAs (microRNAs), for efficient gene silencing. The RNAi pathway is started by the enzyme Dicer, which is a ribonuclease of the RNase III family. This enzyme cleaves long double-stranded RNA (dsRNA) to short double-stranded fragments of 20–25 base pairs. One of the two strands is incorporated into the RNA-induced silencing complex (RISC). The resulting ribonucleoprotein complex (RISC-RNA) lodges itself on the target mRNA by complementary base pairing (between the mRNA and the single-stranded small RNA bound to RISC). This results into degradation of the target mRNA by the argonaute protein. Argonaute is the catalytic component of the RISC complex. The outcome of the whole process is inhibition of gene expression or gene silencing.

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