Catalyzes the transfer of one adenosine molecule from an ATP to an mRNA poly(A) tail bearing a 3'-OH terminal group in an ATP hydrolysis-dependent manner (PubMed:32009146, PubMed:34048638). May be involved in maintaining the translation efficiency of at least some genes through preventing degradation of their mRNAs (PubMed:32009146). Prefers RNA molecules that are adenosine-rich close to 3'-end (PubMed:32009146). In addition, may inhibit cell proliferation and cell cycle progression through ubiquitination of beta-catenin/CTNNB1 (PubMed:30532005). ATP + RNA(n) = diphosphate + RNA(n)-3'-adenine ribonucleotide Uniquely and highly expressed in pre-implantation embryos and pluripotent stem cells, but sharply down-regulated following differentiation. Belongs to the TENT family. It is uncertain whether Met-1 or Met-2 is the initiator. Truncated N-terminus. Truncated N-terminus.