 The passenger strand is degraded and the guide strand is incorporated into the RNA-induced silencing complex (RISC).The most well-studied outcome is post-transcriptional gene silencing, which occurs when the guide strand pairs with a complementary sequence in a messenger RNA molecule and induces cleavage by Argonaute 2 (Ago2), the catalytic component of the RISC.In some organisms, this process spreads systemically, despite the initially limited molar concentrations of siRNA.