How do small RNA molecules, like siRNA and saRNA, function in gene regulation?

Small RNA molecules, such as small interfering RNA (siRNA) and small activating RNA (saRNA), play a crucial role in gene regulation through their ability to modulate gene expression. siRNAs primarily function by targeting specific messenger RNA (mRNA) sequences for degradation, which effectively silences gene expression. They achieve this through a process known as RNA interference (RNAi), where the siRNA guides the RNA-induced silencing complex (RISC) to the complementary mRNA, leading to its destruction.

On the other hand, saRNAs are involved in promoting gene expression rather than silencing it. They can enhance the transcription of specific genes by binding to their promoters, facilitating recruitment of the transcriptional machinery and thus increasing mRNA production.

Therefore, the correct choice reflects the dual role that small RNAs can play—they can induce gene expression in some contexts (as with saRNA) while also silencing genes in other contexts (as with siRNA). This versatility in function underlines the complexity of gene regulation mechanisms and showcases the significance of small RNA molecules in cellular functions.