In wild-type cells, all four of the cellular À1 RF signals and the in-frame PTC containing control were less abundant than the PGK1 reporter mRNA (Figure 2A ). The decrease in mRNA steady-state abundance varied from $100-fold of the readthrough control (EST2) to $0.19-fold of wild-type (TBF1). Experiments were also performed in upf1D and dom34D strains, and the U3 snoRNA-normalized signal intensities were compared among the same signals between wild-type and mutant strains to determine the relative contributions of NMD and NGD on steady-state abundance of the À1 RF signal-containing reporters ( Figure 2B and C). The PTC containing mRNA was only affected through the NMD pathway: 28-fold increased abundance in upf1D cells relative to wild-type cells, but no change in dom34D cells. The TBF1 À1 RF signal similarly affected the reporter signal only through NMD ($4-fold).