Efficient RNA Polyuridylation by Noncanonical Poly(A) Polymerases

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Abstract
Nuclear poly(A) polymerase (PAP) polyadenylates nascent mRNAs, promoting their nuclear export, stability, and translation, while the related cytoplasmic polymerase GLD-2 activates translation of deadenylated mRNAs. Here we characterize the biochemical activity of fission yeast Schizosaccharomyces pombe Cid1, a putative cytoplasmic PAP implicated in cell cycle checkpoint controls. Surprisingly, Cid1 has robust poly(U) polymerase activity in vitro, especially when isolated in native multiprotein complexes. Furthermore, we found that upon S-phase arrest, the 3' ends of actin mRNAs were posttranscriptionally uridylated in a Cid1-dependent manner. Finally, Hs2 (ZCCHC6), a human ortholog of Cid1, shows similar activity. These data suggest that uridylation of mRNA forms the basis of an evolutionarily conserved mechanism of gene regulation.