Poly(A) tail

Poly(A) tail is a stretch of Adenine nucleotides added to the 3' end of an RNA molecule. This modification occurs in most eukaryotic messenger RNA (mRNA) and has significant roles in the regulation of mRNA stability, translation, and nuclear export. The process of adding a poly(A) tail, known as polyadenylation, is part of the post-transcriptional modifications that mRNA undergoes before it is exported from the nucleus to the cytoplasm for translation.

Process of Polyadenylation

Polyadenylation involves the cleavage of the 3' end of the pre-mRNA and the subsequent addition of adenine residues. This process is catalyzed by a complex of proteins, including the enzyme poly(A) polymerase (PAP). The cleavage and polyadenylation specificity factor (CPSF) recognizes a specific hexanucleotide sequence, typically AAUAAA, upstream of the cleavage site, which is crucial for the regulation of poly(A) tail length and, consequently, mRNA stability and translation efficiency.

Functions of the Poly(A) Tail

The poly(A) tail plays several critical roles in mRNA metabolism and function:

• Stability: The length of the poly(A) tail can influence mRNA stability. Longer tails generally protect mRNA from degradation, while shortening of the tail can mark the mRNA for degradation.
• Translation: The presence of a poly(A) tail enhances the translation of mRNA. The interaction between the poly(A) binding protein (PABP) and the translation initiation complex facilitates the circularization of mRNA, promoting efficient translation.
• Nuclear Export: The poly(A) tail, along with certain nuclear export signals, aids in the export of mRNA from the nucleus to the cytoplasm.

Regulation

The length of the poly(A) tail is dynamically regulated through the action of both poly(A) polymerases, which add adenine residues, and deadenylases, which remove them. This regulation is crucial for the control of gene expression in various developmental and cellular processes.

Biological Significance

The poly(A) tail is essential for the proper expression and function of eukaryotic genes. Its role in mRNA stability and translation affects the synthesis of proteins, which is fundamental to all cellular processes. Aberrations in polyadenylation can lead to diseases, including cancer and neurological disorders, highlighting the importance of proper regulation of the poly(A) tail in maintaining cellular health.

See Also

• RNA Splicing
• mRNA Surveillance
• Translation
• Gene Expression