Poly(A) tail

Definition

The poly(A) tail is a sequence of adenine (A) nucleotides added to the 3' end of a mature eukaryotic messenger RNA (mRNA) molecule. This post-transcriptional modification is crucial for the stability, localization, and translation of the mRNA transcript.

5 Must Know Facts For Your Next Test

1. The poly(A) tail protects the mRNA from degradation by exonucleases, increasing its stability and lifespan within the cell.
2. The length of the poly(A) tail can vary, with longer tails generally indicating more stable mRNA transcripts.
3. The poly(A) tail interacts with the 5' cap structure of the mRNA, forming a 'closed loop' that enhances translation efficiency.
4. Polyadenylation is carried out by a complex of enzymes, including the poly(A) polymerase, that recognize specific sequences in the pre-mRNA and add the poly(A) tail.
5. The poly(A) tail plays a role in the nuclear export and cytoplasmic localization of the mRNA, ensuring it reaches the appropriate cellular compartment for translation.

Review Questions

• Explain the importance of the poly(A) tail in the stability and lifespan of mRNA transcripts.
  • The poly(A) tail is a critical feature of mature eukaryotic mRNA molecules that protects them from degradation by cellular exonucleases. By adding a long sequence of adenine nucleotides to the 3' end of the mRNA, the poly(A) tail prevents the mRNA from being rapidly broken down, increasing its stability and lifespan within the cell. This allows the mRNA to be efficiently transported and translated into proteins, supporting the overall process of gene expression.
• Describe the role of the poly(A) tail in enhancing the translation efficiency of mRNA transcripts.
  • The poly(A) tail interacts with the 5' cap structure of the mRNA molecule, forming a 'closed loop' that brings the two ends of the mRNA into close proximity. This circular conformation helps to recruit the translation machinery more efficiently, as the ribosome can easily transition from the 5' end to the 3' end of the mRNA during the translation process. The poly(A) tail-cap interaction also protects the mRNA from degradation, further enhancing its availability for translation and the subsequent production of the encoded protein.
• Analyze the relationship between the length of the poly(A) tail and the stability and localization of mRNA transcripts.
  • The length of the poly(A) tail is directly correlated with the stability and localization of mRNA transcripts. Longer poly(A) tails generally indicate more stable mRNA molecules, as the extended sequence provides greater protection from exonucleases. Additionally, the poly(A) tail plays a role in the nuclear export and cytoplasmic localization of the mRNA, ensuring it reaches the appropriate cellular compartment for translation. Variations in poly(A) tail length can therefore influence the overall lifetime and distribution of mRNA transcripts within the cell, ultimately impacting the expression levels of the encoded proteins.

Related terms

Polyadenylation: The process of adding the poly(A) tail to the 3' end of an mRNA molecule, carried out by a specialized enzyme complex.

Transcription: The process of synthesizing a complementary RNA molecule from a DNA template, the first step in gene expression.

Translation: The process of synthesizing a protein from the information encoded in an mRNA molecule, the final step in gene expression.