Final answer:
RNA interference (RNAi) down-regulates gene expression by directing the degradation of mRNA that is fully complementary to the siRNAs or miRNAs involved in the process.
Step-by-step explanation:
RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression or translation, by neutralizing targeted mRNA molecules. The down-regulation of specific genes via RNAi is a result of the cleavage/degradation of mRNA. This process involves small interfering RNAs (siRNAs) or microRNAs (miRNAs) that bind to mRNA. If the RNA is fully complementary to the target mRNA, it directs the RNA-induced silencing complex (RISC) to degrade the mRNA. This post-transcriptional regulation effectively silences the gene by preventing its translation into protein.
When siRNAs are completely complementary to the target mRNA, they can lead to cleavage and degradation of the mRNA, thereby down-regulating the expression of specific genes. This process is known as gene silencing.