siRNA transcription

Definition

Target type: biologicalprocess

The transcription of a small interfering RNA from an RNA template. [PMID:23001036]

siRNA transcription is the process by which small interfering RNA (siRNA) molecules are produced from double-stranded RNA (dsRNA) precursors. This process is crucial for RNA interference (RNAi), a powerful gene silencing mechanism found in eukaryotes. Here is a detailed description of siRNA transcription:

1. **dsRNA Precursor Synthesis:** The process begins with the generation of a dsRNA precursor molecule. This can occur through various mechanisms, including:
* **Viral infection:** Some viruses, such as RNA viruses, produce dsRNA during their replication cycle.
* **Transfection:** dsRNA can be artificially introduced into cells through transfection methods.
* **Endogenous production:** Some cells can produce dsRNA through endogenous pathways, such as the processing of hairpin-structured RNAs.

2. **Dicer Processing:** The dsRNA precursor is then recognized and processed by a protein complex called Dicer. Dicer is a ribonuclease enzyme that cleaves the dsRNA into short, approximately 21-nucleotide-long fragments. These fragments are known as short interfering RNAs (siRNAs).
* **Dicer specificity:** Dicer preferentially cleaves dsRNA with a 3' overhang of 2 nucleotides.
* **Dicer activity:** Dicer produces siRNAs with a 5' phosphate and a 3' hydroxyl group.

3. **siRNA Duplex Formation:** The siRNA fragments produced by Dicer are double-stranded molecules. Each siRNA molecule consists of a sense strand and an antisense strand.
* **Sense strand:** The sense strand of the siRNA has the same sequence as the target mRNA.
* **Antisense strand:** The antisense strand of the siRNA is complementary to the target mRNA.

4. **RISC Assembly:** The siRNA duplex associates with the RNA-induced silencing complex (RISC). RISC is a multi-protein complex that plays a central role in RNAi.
* **RISC components:** RISC includes proteins such as Argonaute (Ago), which possesses endonuclease activity.
* **Strand selection:** Within RISC, the antisense strand of the siRNA is preferentially selected and incorporated into the active RISC complex.

5. **Target mRNA Recognition and Cleavage:** The antisense strand of the siRNA within RISC guides the complex to the target mRNA. The antisense strand binds to the complementary sequence within the mRNA through base pairing.
* **Target specificity:** The precise sequence complementarity between the antisense strand and the target mRNA ensures high specificity of RNAi.
* **Cleavage:** Once bound to the target mRNA, the Ago protein within RISC cleaves the mRNA molecule, leading to its degradation.

6. **Gene Silencing:** The degradation of the target mRNA prevents the translation of the corresponding gene into a protein. This results in a reduction or complete silencing of gene expression.

In summary, siRNA transcription involves the production of short interfering RNAs (siRNAs) from dsRNA precursors. These siRNAs guide the RNA-induced silencing complex (RISC) to target mRNAs, leading to their cleavage and subsequent gene silencing. The process of siRNA transcription is a vital component of RNA interference, a powerful mechanism that plays a crucial role in regulating gene expression in eukaryotic cells.'
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