Catalytic subunit of the TRAMP complex which has a poly(A) RNA polymerase activity and is involved in a post-transcriptional quality control mechanism limiting inappropriate expression of genetic information. Polyadenylation is required for the degradative activity of the exosome on several of its nuclear RNA substrates like cryptic transcripts generated by RNA polymerase II and III, or hypomethylated pre-tRNAi-Met. Polyadenylates RNA processing and degradation intermediates of snRNAs, snoRNAs and mRNAs that accumulate in strains lacking a functional exosome. TRF4 is also required for proper nuclear division in mitosis, DNA damage repair and sister chromatid cohesion. Involved in the regulation of histone mRNA levels. May mediate mitotic chromosome condensation. ATP + RNA(n) = diphosphate + RNA(n)-3'-adenine ribonucleotide Component of the TRAMP complex (also called TRF4 complex) composed of at least HUL4, MTR4, PAP2/TRF4 and either AIR1 or AIR2. Interacts with NOP53 and POL2. Interacts directly with AIR2. Present with 7550 molecules/cell in log phase SD medium. Belongs to the DNA polymerase type-B-like family. Was originally thought to have DNA polymerase activity.