Rrp6p/Rrp47p constitutes an independent nuclear turnover system of mature small non-coding RNAs in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the nuclear exosome/Rrp6p/TRAMP participates in the 3-end processing of several precursor non-coding RNAs. Here we demonstrate that the depletion of nucleus-specific 3[->]5 exoribonuclease Rrp6p and its cofactor, Rrp47p led to the specific and selective enhancement of steady-state levels of mature small non-coding RNAs (sncRNAs) that include 5S and 5.8S rRNAs, snRNAs and snoRNAs, but not 18S and 25S rRNAs. Most importantly, their steady-state enhancement does not require the exosome, TRAMP, CTEXT, or Rrp6p-associated Mpp6p. Rrp6p/47p-dependent enhancement of the steady-state levels of sncRNAs is associated with the diminution of their nuclear decay-rate and requires their polyadenylation before targeting by Rrp6p, which is catalyzed by both the canonical and non-canonical poly(A) polymerases, Pap1p and Trf4p. Consistent with this finding, we also demonstrated that Rrp6p and Rrp47p exist as an exosome-independent complex. Thus, Rrp6p-Rrp47p defines a core nuclear exosome-independent novel turnover system that targets the small non-coding RNAs.