How tails define the ending: divergent roles for polyadenylation in RNA stability and gene expression

Polyadenylation in eukaryotes has traditionally been viewed as a means of stabilizing mRNAs and enhancing their translation. It is now appreciated, however, that there are multiple pathways to polyadenylation that can have opposing consequences for RNA stability and gene expression. The focus of this article will be on nuclear polyadenylation, highlighting the recent advances in our understanding of noncanonical polyadenylation events and how their outcomes contrast with those of normal mRNA polyadenylation. Much insight into these pathways derives from studies in yeast, although data from metazoans are now emerging which implicate widespread use of polyadenylation as a means of genetic regulation. We show herein that short upstream mRNA polyadenylation events occur in cells undergoing enhanced herpesvirus-mediated mRNA turnover, thereby extending the evidence for poly(A)-stimulated RNA decay in mammals.