polya

PolyA, in molecular biology, refers to the polyadenylate tail—the chain of adenine nucleotides added to the 3' end of most eukaryotic messenger RNAs. The tail is typically dozens to hundreds of nucleotides long and is added after transcription.

Polyadenylation is directed by a general machinery. The polyadenylation signal AAUAAA in the pre-mRNA is recognized by CPSF and CstF, which mark the cleavage site. Cleavage factors CFIm and CF IIm assist, after which poly(A) polymerase (PAP) adds the tail. In the nucleus, the nuclear poly(A) binding protein PABPN1 binds the growing tail to regulate length. Some mRNAs undergo cytoplasmic polyadenylation by GLD-2 family polymerases in response to signals, regulated by cytoplasmic polyadenylation elements (CPE) and CPE-binding protein (CPEB).

Functions: The tail promotes mRNA stability, export, and translation. PABP proteins bound to the tail interact with translation factors to aid ribosome recycling and the formation of a circular mRNA structure that enhances translation initiation. Tail length can influence translation efficiency and is dynamically regulated during development and in response to stimuli.

Deadenylation often initiates decay: CCR4-NOT and PAN2-PAN3 shorten the tail, leading to decapping and 5' to 3' decay by XRN1 or 3' to 5' decay by the exosome.

In bacteria, poly(A) tails more commonly mark RNAs for degradation. Altered polyadenylation is linked to development, cancer, and other diseases, making poly(A) metabolism a focus of research.