Global view on the metabolism of RNA poly(A)-tails in yeast Saccharomyces cerevisiae

The polyadenosine tail (poly[A]-tail) is a universal modification of eukaryotic messenger RNAs (mRNAs) and non-coding RNAs (ncRNAs). In budding yeast, Pap1-synthesized mRNA poly(A)-tails enhance export and translation, whereas the Trf4/5-mediated polyadenylation of ncRNAs facilitates degradation by the exosome. Using Direct RNA Sequencing, we decipher the extent of poly(A)-tail dynamics in yeast defective of all relevant exonucleases, deadenylases, and poly(A)-polymerases. Predominantly ncRNA poly(A)-tails are 20-60 As long. Poly(A)-tails of newly made mRNAs are 50 adenosine long on average with a upper limit of 200 As. Extensive exonucleolysis by Trf5-assisted nuclear exosome and cytoplasmic deadenylases trim mRNA poly(A)-tails to the lengths of 40 adenosines on average. Surprisingly PAN2/3 and CCR4-NOT deadenylase complexes have a large pool of non-overlapping substrates mainly defined by expression level. Finally, we demonstrate that mRNA poly(A)-tail length strongly responds to growth conditions such as heat and nutrient deprivation.