What are small interfering RNA (siRNA) primarily involved in?

Small interfering RNA (siRNA) play a crucial role in the RNA interference (RNAi) pathway, which is a biological process used by cells to regulate gene expression. SiRNA are specifically involved in the silencing of gene expression by binding to complementary messenger RNA (mRNA) and promoting its degradation. This mechanism is significant for gene regulation, viral defense, and maintaining genome integrity.

The process begins with long double-stranded RNA being processed into siRNA by the enzyme Dicer. The resulting siRNAs are then incorporated into a protein complex known as RISC (RNA-induced silencing complex). Within this complex, the siRNA guides the RISC to its target mRNA, leading to its cleavage and subsequent degradation. This results in a decrease in the expression of specific genes, which is why siRNA are characterized as functional intermediates of RNA interference.

Other potential roles mentioned in the alternatives do not accurately depict the primary function of siRNA within cellular processes. Gene activation at the transcriptional level predominantly involves other types of RNA and transcription factors, while breakdown of nucleic acid molecules is a broader category that includes processes beyond the scope of what siRNA specifically achieves. Additionally, joining DNA fragments during replication is an action performed by enzymes like DNA ligase