Poly(A) tail

Definition

The poly(A) tail is a stretch of adenine nucleotides added to the 3' end of a pre-mRNA molecule during RNA processing in eukaryotic cells. This modification plays a crucial role in stabilizing the mRNA, facilitating its export from the nucleus, and enhancing its translation efficiency by aiding ribosome recognition.

5 Must Know Facts For Your Next Test

1. The poly(A) tail is typically 50 to 250 adenine nucleotides long and is added by an enzyme called poly(A) polymerase after transcription.
2. It enhances the stability of mRNA by protecting it from exonuclease degradation in the cytoplasm.
3. The length of the poly(A) tail can vary between different mRNAs and affects their translation efficiency; longer tails usually lead to increased protein synthesis.
4. During mRNA degradation, the poly(A) tail is gradually shortened, which signals the mRNA for decay.
5. Poly(A) tails are also involved in the regulation of gene expression, influencing how much protein is produced from a given mRNA.

Review Questions

• How does the poly(A) tail contribute to the stability and translation of mRNA?
  • The poly(A) tail enhances mRNA stability by protecting it from degradation by exonucleases. This extension allows the mRNA to have a longer lifespan within the cytoplasm, increasing the likelihood that it will be translated into protein. Additionally, the poly(A) tail helps ribosomes recognize and bind to the mRNA more effectively, promoting efficient translation.
• Discuss the role of the poly(A) tail in the overall RNA processing mechanism in eukaryotic cells.
  • The poly(A) tail is a key modification that occurs during RNA processing in eukaryotes alongside capping and splicing. After transcription, enzymes add this tail to the 3' end of pre-mRNA. This step is crucial as it not only stabilizes the mRNA but also signals that the RNA has been properly processed and is ready for export from the nucleus. The presence of a poly(A) tail is essential for ensuring that only mature and properly modified mRNAs are translated.
• Evaluate the implications of variations in poly(A) tail length on gene expression and protein synthesis.
  • Variations in poly(A) tail length can significantly impact gene expression and protein synthesis. Longer poly(A) tails typically correlate with increased translation efficiency, meaning that proteins are synthesized at higher rates. Conversely, shorter tails may lead to quicker degradation of mRNA, resulting in lower protein output. This regulatory mechanism allows cells to fine-tune protein levels in response to various signals, making it an important aspect of post-transcriptional control of gene expression.

Related terms

5' Cap: A modified guanine nucleotide added to the 5' end of eukaryotic mRNA, which protects the RNA from degradation and assists in ribosome binding during translation.

Splicing: The process of removing introns and joining exons in pre-mRNA to produce a mature mRNA molecule that can be translated into a protein.

mRNA stability: The lifespan of mRNA molecules in the cell, which affects how long they can be translated into proteins and is influenced by various modifications, including the poly(A) tail.