polyadenylated

Polyadenylated describes RNA transcripts that carry a poly(A) tail, a stretch of adenosine nucleotides added to the 3' end of the molecule. In eukaryotes, most nuclear-encoded mRNAs are polyadenylated after transcription as part of 3' end processing, which involves cleavage of the pre-mRNA upstream of a polyadenylation signal and subsequent addition of the tail.

The addition is carried out by poly(A) polymerase and requires a cohort of processing factors, including cleavage and polyadenylation specificity factor (CPSF) and cleavage stimulation factor (CstF). The resulting poly(A) tail is bound by poly(A)-binding proteins (PABP), which interact with other translation factors to promote mRNA circularization and efficient translation, while also protecting the transcript from exonucleolytic decay. Tail length varies but is commonly in the range of a few dozen to a few hundred nucleotides; in mammals, tails are often around 200 nucleotides, whereas yeast tails tend to be shorter. Tail length can influence mRNA stability and translational efficiency and is tightly regulated during development and in response to cellular signals.

Alternative polyadenylation uses different poly(A) sites to produce mRNA isoforms with distinct 3' untranslated regions, affecting localization, regulation by microRNAs, and protein production without altering the encoded protein.

Not all RNAs are polyadenylated. Histone mRNAs, for example, lack poly(A) tails and end in a conserved stem-loop structure that regulates their expression. Some noncoding RNAs also lack poly(A) tails, while others may be oligoadenylated under certain conditions to target them for decay.