**2.4 Mechanisms of bifunctional shRNA**

Bifunctional shRNA can make use of cleavage-dependent and non cleavage-dependent RNAi (Rao *et al,* 2010). Such shRNA contains two stem loops: one with complete-matching passenger and guide strands, which can combine with cleavage-dependent RISC, and the other with non-matching strands, which can combine with non cleavage-dependent RISC. This shRNA is more efficient than shRNA RNAi with one RISC complex. In experiments directly comparing the same siRNA target RNAi, it was found that bifunctional shRNA was more efficient (the same dosage of shRNA could produce more powerful gene knockout function) and its pharmacokinetics also underwent change(Rao *et al,* 2009,2010).
