post-transcriptional gene silencing

Definition

Target type: biologicalprocess

The inactivation of gene expression that occurs after transcription. [GOC:mah, PMID:15020054]

Post-transcriptional gene silencing (PTGS) is a fundamental regulatory mechanism in eukaryotic cells that involves the targeted degradation or repression of mRNA molecules, thereby preventing the translation of specific genes into proteins. PTGS is a complex process that involves several key steps, including:

1. **Initiation:** PTGS is typically triggered by the presence of double-stranded RNA (dsRNA), which can originate from viral infections, transposon activity, or even endogenous gene expression. dsRNA is recognized by specific cellular proteins, such as Dicer, an RNase III enzyme.

2. **Dicer Processing:** Dicer cleaves dsRNA into short, double-stranded fragments called small interfering RNAs (siRNAs) or microRNAs (miRNAs). These siRNAs and miRNAs are typically 20-25 nucleotides in length and have a characteristic 5' phosphate and 3' hydroxyl group.

3. **RISC Assembly:** The siRNAs or miRNAs are then loaded into a multi-protein complex known as the RNA-induced silencing complex (RISC). RISC is a highly dynamic complex that contains several key proteins, including Argonaute proteins, which are responsible for recognizing and binding to target mRNAs.

4. **Target Recognition:** The siRNA or miRNA within RISC guides the complex to target mRNAs based on sequence complementarity. The degree of complementarity between the siRNA/miRNA and the target mRNA determines the outcome of silencing.

5. **mRNA Degradation or Repression:** If the siRNA or miRNA perfectly complements the target mRNA, RISC promotes the degradation of the mRNA by recruiting cellular nucleases. This process is known as "slicing." In cases of imperfect complementarity, RISC primarily blocks translation of the target mRNA, leading to a reduction in protein production.

Overall, PTGS plays a critical role in regulating gene expression, controlling viral infection, and maintaining genome stability. This sophisticated mechanism provides cells with a powerful tool to fine-tune gene expression and adapt to changing environments.'
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Proteins (1)

Compounds (3)