Exonucleases and endonucleases involved in polyadenylation-assisted RNA decay.

RNA polyadenylation occurs in most forms of life, excluding a small number of biological systems. This posttranscriptional modification undertakes two roles, both of which influence the stability of the polyadenylated transcript. One is associated with the mature 3' ends of nucleus-encoded mRNAs in eukaryotic cells and is important for nuclear exit, translatability, and longevity. The second form of RNA polyadenylation assumes an almost opposite role; it is termed 'transient' and serves to mediate the degradation of RNA. Poly(A)-assisted RNA decay pathways were once thought to occur only in prokaryotes/organelles but are now known to be a common phenomenon, present in bacteria, organelles, archaea, and the nucleus and cytoplasm of eukaryotic cells, regardless of the fact that in some of these systems, stable polyadenylation exists as well. This article will summarize the current knowledge of polyadenylation and degradation factors involved in poly(A)-assisted RNA decay in the domains of life, focusing mainly on that which occurs in prokaryotes and organelles. In addition, it will offer an evolutionary view of the development of RNA polyadenylation and degradation and the cellular machinery that is involved.