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poly A tail

noun

It is a long stretch of (about ten to 200 or more) adenine nucleotides added to the "tail" or 3' end of the pre-mRNA via the process called polyadenylation catalyzed by the enzyme, polyadenylate polymerase (PAP).

In eukaryotic organisms, most messenger RNA molecules end with a poly-A stretch at their 3' ends. It is believed to protect the mRNA from degradation by exonucleases, and is essential for transcription termination, for export of the mRNA from the nucleus, and for translation.