Terminal nucleotidyltransferase that catalyzes preferentially the transfert of ATP and GTP on RNA 3' poly(A tail creating a heterogeneous 3' poly(A tail leading to mRNAs stabilization by protecting mRNAs from active deadenylation. Also functions as a catalytic subunit of a TRAMP-like complex which has a poly(A RNA polymerase activity and is involved in a post-transcriptional quality control mechanism. Polyadenylation with short oligo(A tails is required for the degradative activity of the exosome on several of its nuclear RNA substrates. Doesn't need a cofactor for polyadenylation activity (in vitro. Required for cytoplasmic polyadenylation of mRNAs involved in carbohydrate metabolism, including the glucose transporter SLC2A1/GLUT1. Plays a role in replication-dependent histone mRNA degradation, probably through terminal uridylation of mature histone mRNAs. May play a role in sister chromatid cohesion. Mediates 3' adenylation of the microRNA MIR21 followed by its 3'-to-5' trimming by the exoribonuclease PARN leading to degradation. Mediates 3' adenylation of H/ACA box snoRNAs (small nucleolar RNAs followed by its 3'-to-5' trimming by the exoribonuclease PARN which enhances snoRNA stability and maturation.