Non-catalytic component of the RNA exosome complex which has 3'->5' exoribonuclease activity and participates in a multitude of cellular RNA processing and degradation events. In the nucleus, the RNA exosome complex is involved in proper maturation of stable RNA species such as rRNA, snRNA and snoRNA, in the elimination of RNA processing by-products and non-coding 'pervasive' transcripts, such as antisense RNA species and cryptic unstable transcripts (CUTs), and of mRNAs with processing defects, thereby limiting or excluding their export to the cytoplasm. In the cytoplasm, the RNA exosome complex is involved in general mRNA turnover and in RNA surveillance pathways, preventing translation of aberrant mRNAs. The catalytic inactive RNA exosome core complex of 9 subunits (Exo-9) is proposed to play a pivotal role in the binding and presentation of RNA for ribonucleolysis, and to serve as a scaffold for the association with catalytic subunits and accessory proteins or complexes. RRP42 is part of the hexameric ring of RNase PH domain-containing subunits proposed to form a central channel which threads RNA substrates for degradation. Component of the RNA exosome complex. Specifically part of the catalytically inactive RNA exosome core (Exo-9) complex which associates with catalytic subunits DIS3 and RRP6 in cytoplasmic- and nuclear-specific RNA exosome complex forms. Exo-9 is formed by a hexameric ring of RNase PH domain-containing subunits and peripheral S1 domain-containing components CSL4, RRP4 and RRP40 located on the top of the ring structure. Present with 7110 molecules/cell in log phase SD medium. Belongs to the RNase PH family.