Poly-A tail

Poly-A tail is a stretch of RNA that has only adenine bases. In eukaryotic organisms, a poly-A tail is added to the 3' end of the pre-mRNA once elongation is complete. The poly-A tail protects the mRNA from degradation, aids in the export of the mature mRNA to the cytoplasm, and is involved in binding proteins involved in initiating translation.

Function

The polyadenylation signal in the DNA of a gene codes for the addition of the poly-A tail to the pre-mRNA. The poly-A tail is added to the pre-mRNA in the nucleus before the RNA is transported to the cytoplasm. The poly-A tail protects the mRNA molecule from enzymatic degradation in the cytoplasm and aids in transcription termination, export of the mRNA from the nucleus, and translation.

Structure

The poly-A tail is a long chain of adenine nucleotides (hence, poly-A) that is added to a messenger RNA (mRNA) molecule during RNA processing to increase the stability of the molecule. The length of the tail varies with the species and developmental stage, but can be up to several hundred nucleotides long.

Role in Translation

The poly-A tail is important in the initiation of protein synthesis. The eukaryotic initiation factor (eIF4G) of the translation machinery binds to the poly-A binding protein (PABP) which has bound to the poly-A tail of the mRNA. This circularizes the mRNA and allows for re-initiation of protein synthesis.

See Also

• Messenger RNA
• RNA processing
• Translation (biology)

Poly-A tail Resources
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