In eukaryotes, polyadenylation of pre-mRNA plays an essential role in the initiation step of protein synthesis, as well as in the export and stability of mRNAs. Poly(A) polymerase, the enzyme at the heart of the polyadenylation machinery, is a template-independent RNA polymerase which specifically incorporates ATP at the 3' end of mRNA [1]. The N-terminal catalytic domain of Poly(A) polymerase is a member of the nucleotidyltransferase superfamily [1].

1: Crystal structure of mammalian poly(A) polymerase in complex with an analog of ATP. Martin G, Keller W, Doublie S; EMBO J 2000;19:4193-4203. PMID:10944102