Figure 2.

Depletion of TRAPP abolishes the Ypt1p exchange activity from cytosol. TRAPP was depleted by incubating IgG-Sepharose beads with cytosol prepared from a strain in which Bet3p is Protein A tagged and the DSS4 gene is deleted. Samples containing 0.2 mg of mock-treated or 0.5 mg of IgG-Sepharose–treated cytosol were resolved by SDS-PAGE and analyzed by Western blot analysis with α-Trs33p serum (C). TRAPP-depleted or mock-treated cytosol was incubated with 5 pmol of Ypt1p (A) or Ypt32p (B) preloaded with [³H]GDP. At the time intervals indicated, radioactivity that bound to protein was determined by filter-binding, and the data are expressed as the percentage of label bound to Ypt1p or Ypt32p. The intrinsic rate of [³H]GDP release from Ypt1p or Ypt32p was measured in the presence of BSA.