Fig. 4. Acceleration of 3′-to-5′ directed NMD is mediated through Upf proteins. Yeast strains lacking XRN1 and/or UPF genes (xrn1Δ, YS064; xrn1Δ upf1Δ, YS070; xrn1Δ upf2Δ YS071; xrn1Δ upf3Δ, YS072), which carry PGK1N103pG (A) and PGK1pG (B) reporters, were grown at 25°C in the galactose medium to mid-log phase. Transcriptional repression and hybridization were performed as described for Figure 1. The half-lives (t1/2; min) of mRNAs are shown as means ± SD, which were obtained from at least three independent experiments.