ATP-dependent RNA helicase required for the 3'-end formation of 5.8S RNA. Cofactor for the exosome complex that unwinds secondary structure in pre-rRNA. Required for nucleocytoplasmic transport of mRNA. May serve as a chaperone which translocates or normalizes the structure of mRNAs in preparation for export. 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. ATP + H2O = ADP + H(+) + phosphate Component of the TRAMP complex (also called TRF4 complex) composed of at least HUL4, MTR4, PAP2/TRF4 and either AIR1 or AIR2. Present with 12500 molecules/cell in log phase SD medium. Belongs to the helicase family. SKI2 subfamily.