Uridylation Earmarks mRNAs for Degradation… and More.

Groundbreaking discoveries have uncovered the widespread post-transcriptional modifications of all classes of RNA. These studies have led to the emerging notion of an 'epitranscriptome' as a new layer of gene regulation. Diverse modifications control RNA fate, including the 3' addition of untemplated nucleotides or 3' tailing. The most exciting recent discoveries in 3' tailing are related to uridylation. Uridylation targets various noncoding RNAs, from small RNAs and their precursors to rRNAs, and U tails mostly regulate processing or degradation. Interestingly, uridylation is also a pervasive modification of mRNAs. In this review, we discuss how the addition of few uridines to the 3' end of mRNAs influences mRNA decay. We also consider recent findings that reveal other consequences of uridylation on mRNA fate.