Polyadenylointiin

Polyadenylointiin is a biological process that occurs in eukaryotic cells. It refers to the addition of a tail of adenosine residues to the 3' end of messenger RNA (mRNA) molecules. This tail, known as the poly(A) tail, is not encoded in the DNA template but is added by an enzyme called poly(A) polymerase after transcription. The process begins with the cleavage of the pre-mRNA molecule at a specific site. Following cleavage, the poly(A) polymerase adds approximately 250 adenosine nucleotides to the newly formed 3' end.

The poly(A) tail plays several crucial roles in gene expression. It protects the mRNA from degradation by exonucleases, thereby increasing its stability and lifespan in the cytoplasm. This stability is important for ensuring that sufficient protein can be synthesized from the mRNA molecule. Furthermore, the poly(A) tail is involved in the export of mRNA from the nucleus to the cytoplasm, where protein synthesis takes place. It also plays a role in the translation initiation process, helping ribosomes bind to the mRNA and begin protein synthesis. The length of the poly(A) tail can vary, and its shortening over time can signal the eventual degradation of the mRNA. This dynamic regulation of mRNA stability and translation is a key aspect of cellular control.