Upf1p, Nmd2p, and Upf3p regulate the decapping and exonucleolytic degradation of both nonsense-containing mRNAs and wild-type mRNAs

In Saccharomyces cerevisiae, rapid degradation of nonsense containing mRNAs requires the decapping enzyme Dcp1p, the 5'-to-3' exoribonuclease Xrn1p, a nd the three nonsense-mediated mRNA decay (NMD) factors, Upf1p, Nmd2p, and Upf3p. To identify specific functions for the NMD factors, we analyzed the mRNA decay phenotypes of yeast strains containing deletions of DCP1 or XRN1 and UPF1, NMD2, or UPF3. Our results indicate that Upf1p, Nmd2p, and Upf3p regulate decapping and exonucleolytic degradation of nonsense-containing m RNAs. In addition,we show that these factors also regulate the same process es in the degradation of wild-type mRNAs. The participation of the NMD fact ors in general mRNA degradation suggests that they may regulate an aspect o f translation termination common to all transcripts.