Polyadenylated versions of small non-coding RNAs in Saccharomyces cerevisiae are degraded by Rrp6p/Rrp47p independent of the core nuclear exosome

Abstract

In Saccharomyces cerevisiae, polyadenylated forms of mature (and not precursor) small non coding RNAs (sncRNAs) those fail to undergo proper 3' end maturation are subject to an active degradation by Rrp6p and Rrp47p, which does not require the involvement of core exosome and TRAMP components. In agreement with this finding, Rrp6p/Rrp47p is demonstrated to exist as an exosome-independent complex, which preferentially associates with mature polyadenylated forms of these sncRNAs. Consistent with this observation, a C-terminally truncated version of Rrp6p (Rrp6p AC2) lacking physical association with the core nuclear exosome supports their decay just like its full length ver sion. Polyadenylation is catalyzed by both the canonical and non canonical poly(A) polymerases, Paplp and Trf4p. Analysis of the polyadenylation profiles in WT and rrp6-A strains revealed that the majority of the polyadenylation sites correspond to either one to three nucleotides upstream or downstream of their mature ends and their poly(A) tails ranges from 10 15 adenylate residues. Most interestingly, the accumulated polyadenylated snRNAs are functional in the rrp& A strain and are assembled into spliceosomes. Thus, Rrp6p Rrp47p defines a core nuclear exosome-independent novel RNA turnover system in baker's yeast targeting imperfectly processed polyadenylated sncRNAs that accumulate in the absence of Rrp6p.