Final answer:
RNA interference (RNAi) is induced by small interfering RNAs (siRNAs) or microRNAs (miRNAs), molecules that bind to and silence specific mRNA molecules, preventing protein synthesis.
Step-by-step explanation:
The type of molecule that triggers RNA interference (RNAi) is either a small interfering RNA (siRNA) or a microRNA (miRNA). These molecules are central to the RNAi pathway and function through binding to and silencing specific mRNA molecules, thereby preventing protein synthesis. siRNAs and miRNAs differentiate primarily in their degree of complementarity to their target mRNA; siRNAs are completely complementary, leading to mRNA cleavage, whereas miRNAs are mostly complementary and generally inhibit translation without cleavage unless they are fully complementary to the mRNA target. The RNAi mechanism is a powerful tool for researchers developing treatments for viral infections, due to its ability to precisely silence genes within eukaryotic cells.