poly-A tail

The poly-A tail is a long chain of adenine nucleotides that is added to a messenger RNA (mRNA) molecule during RNA processing to increase the stability of the molecule. Immediately after a gene in a eukaryotic cell is transcribed, the new RNA molecule undergoes several modifications known as RNA processing. These modifications alter both ends of the primary RNA transcript to produce a mature mRNA molecule. The processing of the 3' end adds a poly-A tail to the RNA molecule. First, the 3' end of the transcript is cleaved to free a 3' hydroxyl. Then an enzyme called poly-A polymerase adds a chain of adenine nucleotides to the RNA. This process, called polyadenylation, adds a poly-A tail that is between 100 and 250 residues long. The poly-A tail makes the RNA molecule more stable and prevents its degradation. Additionally, the poly-A tail allows the mature messenger RNA molecule to be exported from the nucleus and translated into a protein by ribosomes in the cytoplasm.