polüadenüülatsioon

Polyadenylation is a crucial process in gene expression, specifically in the maturation of messenger RNA (mRNA) in eukaryotic cells. It involves the addition of a tail of adenine nucleotides, known as a poly(A) tail, to the 3' end of a pre-mRNA molecule. This tail is typically between 50 to 250 nucleotides long.

The process of polyadenylation occurs after transcription, where the RNA polymerase has synthesized the initial RNA strand. Specific sequences within the pre-mRNA, such as the AAUAAA signal, are recognized by a complex of proteins. This complex cleaves the pre-mRNA at a specific site downstream of the recognition signal. Following cleavage, an enzyme called poly(A) polymerase (PAP) adds the adenine nucleotides one by one to the newly formed 3' end, without the need for a template.

The poly(A) tail serves several important functions. It enhances the stability of the mRNA molecule, protecting it from degradation by cellular nucleases. This increased stability allows the mRNA to persist in the cytoplasm for a longer period, enabling more protein synthesis. Furthermore, the poly(A) tail plays a role in the export of mRNA from the nucleus to the cytoplasm. It also facilitates the initiation of translation by interacting with proteins involved in the ribosome binding process. Without polyadenylation, mRNA molecules would be unstable and inefficiently translated, significantly impacting protein production within the cell.