RNA-induced silencing complex

Definition

The RNA-induced silencing complex (RISC) is a multi-protein complex that plays a crucial role in post-transcriptional regulation of gene expression. It facilitates the process of RNA interference (RNAi) by incorporating small RNA molecules, like microRNAs (miRNAs) or small interfering RNAs (siRNAs), which guide RISC to target messenger RNAs (mRNAs) for degradation or translational repression. This mechanism is essential for controlling gene expression, maintaining cellular homeostasis, and defending against viral infections.

5 Must Know Facts For Your Next Test

1. RISC is formed when double-stranded RNA is processed into small RNA fragments by the enzyme Dicer, which then incorporates one strand into the complex.
2. Once loaded into RISC, the small RNA guides the complex to complementary mRNA targets based on sequence homology, leading to mRNA degradation or translational inhibition.
3. RISC not only participates in regulating gene expression but also plays a role in antiviral defense by targeting viral RNAs for degradation.
4. The activity of RISC can be modulated by various proteins that interact with it, influencing its ability to silence specific genes.
5. Dysregulation of RISC components or pathways can lead to diseases such as cancer, where improper gene silencing contributes to uncontrolled cell growth.

Review Questions

• How does RISC utilize small RNA molecules to influence gene expression at the post-transcriptional level?
  • RISC utilizes small RNA molecules like miRNAs and siRNAs to guide its activity in regulating gene expression. When RISC incorporates a small RNA, it can recognize complementary sequences on target mRNAs. This recognition allows RISC to either promote the degradation of the mRNA or inhibit its translation, effectively silencing the gene associated with that mRNA and impacting protein production within the cell.
• Discuss the mechanisms by which RISC can mediate both mRNA degradation and translational repression.
  • RISC can mediate mRNA degradation through endonucleolytic cleavage or by promoting the deadenylation of the target mRNA, which leads to its decay. Alternatively, RISC can induce translational repression by preventing ribosome assembly on the mRNA or causing ribosomal stalling. These mechanisms allow RISC to exert precise control over protein synthesis in response to cellular needs and external signals.
• Evaluate the implications of RISC dysfunction in human diseases, particularly cancer.
  • Dysfunction of RISC can have significant implications for human diseases, especially cancer. When components of RISC are mutated or misregulated, it can lead to improper silencing of tumor suppressor genes or insufficient silencing of oncogenes. This dysregulation contributes to uncontrolled cell proliferation and resistance to apoptosis. Understanding these pathways offers potential therapeutic avenues for targeting aberrant RISC function in cancer treatments.

Related terms

RNA interference: A biological process where RNA molecules inhibit gene expression by causing the degradation of specific mRNA transcripts.

MicroRNA: Small, non-coding RNA molecules that regulate gene expression by binding to complementary sequences on target mRNAs, often leading to their degradation.

Small interfering RNA: Short double-stranded RNA molecules that play a key role in the RNAi pathway, guiding RISC to target and degrade specific mRNA sequences.