Final answer:
Poly-adenylation in eukaryotes occurs during mRNA processing after transcription. The poly(A) tail functions to assist in mRNA transport and regulate mRNA stability in the cytoplasm, as well as protect the mRNA from degradation.
Step-by-step explanation:
In eukaryotes, poly-adenylation occurs during mRNA processing after transcription. Once elongation is complete, an endonuclease cleaves the pre-mRNA between an AAUAAA consensus sequence and a GU-rich sequence, leaving the AAUAAA sequence on the pre-mRNA. Then, an enzyme called poly-A polymerase adds a string of approximately 200 adenine residues, called the poly-A tail.
The function of the poly(A) tail includes assisting in the transport of mRNAs from the nucleus to the cytoplasm and regulating the stability of mRNAs in the cytoplasm. The poly(A) tail also protects the mRNA from degradation by enzymes in the cytoplasm.