What type of nucleotides are found at the end of the Poly A tail?

The Poly A tail is a sequence of adenine nucleotides added to the 3' end of a primary RNA transcript during RNA processing. This tail plays a critical role in stabilizing the mRNA molecule, protecting it from degradation, and facilitating its export from the nucleus to the cytoplasm. In eukaryotic cells, the presence of the Poly A tail is a defining feature of mRNA and is important for mRNA stability and translation efficiency.

The reason adenine nucleotides make up the Poly A tail is due to the enzyme polyadenylate polymerase, which specifically adds these adenine residues after the transcription of a gene is completed. This process ensures that the resulting mRNA has a functional Poly A tail, which is essential for its lifecycle.