Exosome non-catalytic core component; involved in 3'-5' RNA processing and degradation in both the nucleus and the cytoplasm; protein abundance increases in response to DNA replication stress; has similarity to E. coli RNase PH; human ortholog hRrp45p (PM/SCL-75, EXOSC9) complements the yeast null mutant; mutations in hRrp45p are implicated in pontocerebellar hypoplasia type 1D