RNA-induced silencing complex (RISC)

Definition

The RNA-induced silencing complex (RISC) is a multi-protein complex that plays a crucial role in gene regulation by facilitating the process of RNA interference (RNAi). RISC binds to small RNA molecules, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), and uses them as guides to recognize and silence complementary mRNA targets, effectively preventing their translation into proteins. This mechanism is vital for post-transcriptional regulation, as it helps control gene expression in response to various cellular signals and environmental factors.

5 Must Know Facts For Your Next Test

1. RISC is essential for the mechanism of RNA interference, which is used by cells to regulate gene expression and defend against viral infections.
2. The core component of RISC is the Argonaute protein, which binds to small RNA molecules and is responsible for the recognition of target mRNAs.
3. RISC can lead to mRNA degradation or translational repression depending on the degree of complementarity between the small RNA and the target mRNA.
4. The assembly of RISC occurs in the cytoplasm after the processing of precursor RNAs into small RNA duplexes by the Dicer enzyme.
5. RISC plays a role in various biological processes, including development, differentiation, and response to stress, showcasing its importance in cellular regulation.

Review Questions

• How does RISC utilize small RNA molecules to regulate gene expression?
  • RISC utilizes small RNA molecules, like miRNAs and siRNAs, as guides to identify specific mRNA targets based on sequence complementarity. Once RISC is bound to its small RNA, it can either degrade the target mRNA or inhibit its translation, thus effectively silencing the gene. This process allows cells to finely tune gene expression in response to various signals and stresses.
• Discuss the significance of RISC in the context of cellular defense mechanisms against viral infections.
  • RISC plays a vital role in the cellular defense against viral infections by utilizing siRNAs derived from viral RNA. When a cell is infected by a virus, it can produce siRNAs that target viral mRNA for degradation. By silencing viral genes through the action of RISC, cells can limit viral replication and spread, showcasing an important aspect of innate immunity.
• Evaluate how dysregulation of RISC activity could contribute to disease states such as cancer.
  • Dysregulation of RISC activity can lead to aberrant gene expression patterns that contribute to disease states like cancer. For instance, if RISC fails to properly silence oncogenes or if tumor suppressor genes are not expressed due to defective miRNA regulation, it can result in uncontrolled cell proliferation and tumorigenesis. Furthermore, changes in RISC components or small RNA levels can disrupt normal cellular pathways, enhancing the aggressiveness of cancer cells and complicating treatment options.

Related terms

MicroRNA (miRNA): A class of small non-coding RNA molecules that regulate gene expression by binding to target mRNAs, leading to their degradation or inhibition of translation.

Small interfering RNA (siRNA): Short double-stranded RNA molecules that play a key role in the RNA interference pathway by guiding RISC to complementary mRNA targets for degradation.

RNA interference (RNAi): A biological process in which small RNA molecules inhibit gene expression or translation, effectively silencing specific genes in a sequence-specific manner.