Effects of Δupf1, Δupf2 mutations and correction of these mutants on the stability of selected mRNAs. 4TU RNA from wt, Δupf1, Δupf1 his-3::upf1, Δupf1 his-3::upf1-3XFLAG strains (A) or Δupf2, Δupf2 his-3::upf2-3XFLAG and Δupf2, his-3::upf2-HAT-FLAG strains (B) were analyzed by pulse–chase for arg-2, cox-5, upf1, upf2, eif4a3, erf1, and eif5 mRNAs using the procedures described in Figure 2. See also Figure S6.