Non-catalytic component of the exosome, which is a complex involved in RNA degradation. Increases the RNA binding and the efficiency of RNA degradation. Confers strong poly(A) specificity to the exosome. Component of the archaeal exosome complex. Forms a trimer of Rrp4 and/or Csl4 subunits. The trimer associates with a hexameric ring-like arrangement composed of 3 Rrp41-Rrp42 heterodimers. Contains an N-terminal domain that mediates interactions with the hexameric ring, a central S1 domain and a C-terminal KH domain. The KH domain is required for efficient RNA degradation, but is not responsible for poly(A) preference. Belongs to the RRP4 family.