Final answer:
siRNA directed against the living mRNA leads to gene silencing through RNA interference (RNAi).
Step-by-step explanation:
When small interfering RNA (siRNA) is directed against the complementary mRNA transcript of a specific gene, it can lead to gene silencing through a process called RNA interference (RNAi). siRNA is completely complementary to the mRNA and it binds to the RNA-induced silencing complex (RISC). The siRNA-RISC complex then binds to the mRNA and cleaves it, preventing translation and protein synthesis. This process is used to control gene expression and is being investigated as a potential therapeutic tool.