mRNAs containing premature translation termination codons (nonsense mRNAs) are targeted for deadenylation-independent degradation in a mechanism that depends on Upf1p, Upf2p and Upf3p. This decay pathway is often called nonsense-mediated mRNA decay (NMD). Nonsense mRNAs are decapped by Dcp1p and then degraded 5′ to 3′ by Xrn1p. In the yeast Saccharomyces cerevisiae, a significant number of wild-type mRNAs accumulate in upf mutants. Wild-type PPR1 mRNA is one of these mRNAs. Here we show that PPRI mRNA degradation depends on the Upf proteins, Dcp1p, Xrn1p and Hrp1p. We have mapped an Upf1p-dependent destabilizing element to a region located within the 5′-UTR and the first 92 bases of the PPR1 ORF. This element targets PPR1 mRNA for Upf-dependent decay by a novel mechanism.
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