Figure 1.

Biological principle of RNA interference: 1. siRNA-pathway: RdRPs generate long dsRNA from single-stranded RNA templates, that are taken up by endocytosis and processed into siRNA by Dicer or TRBP which is loaded onto RISC. 2. miRNA-pathway: RNAPol II transcribes pri-miRNA, which is processed by RNAse III and DGCR8 protein to pre-miRNA. Pre-miRNA is exported by exportin 5 and processed by Dicer to dsmiRNA, which is loaded onto RISC. The passenger strand is degraded, and the guide strand can bind the target sequence and alter gene expression, by cleavage, methylation, translation inhibition, etc.