How does RNA interference (RNAi) function?

RNA interference (RNAi) is a crucial biological process that regulates gene expression and is primarily recognized for its ability to selectively degrade mRNA transcripts. The mechanism begins when double-stranded RNA (dsRNA) is introduced into a cell, which can come from various sources, including viruses or artificially synthesized sequences. The dsRNA is processed by an enzyme called Dicer into smaller fragments known as small interfering RNAs (siRNAs).

These siRNAs are then incorporated into a protein complex called the RNA-induced silencing complex (RISC). Within this complex, the siRNA strands guide the RISC to complementary mRNA targets. Once bound, the RISC cleaves the mRNA, effectively preventing it from being translated into proteins. This process not only silences specific genes but also plays a significant role in cellular defense against viruses and the regulation of gene expression levels.

The other options do not accurately represent the function of RNA interference: enhancing protein translation, increasing gene expression, or modifying DNA sequences are not direct mechanisms involved in RNAi. Instead, RNAi specifically targets and degrades mRNA, leading to a decrease in protein production from those mRNA transcripts.