Component 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 (By similarity). Required for heterochromatic gene silencing at centromeric repeats by either exosome- or RNAi-mediated degradation of heterochromatic transcripts. Component of the TRAMP complex (also called TRF4 complex) composed of at least cid14, mtr4, and air1. Belongs to the helicase family. SKI2 subfamily.