Figure 4.

The ICFP is not subject to ERAD but is subject to degradation by vacuolar proteases. (A) The ICFP was expressed from the GPD1 promoter in a sec18-1 mutant strain where the ICFP cannot reach the Golgi complex. Cells were preincubated at the restrictive temperature (37°C) for 10 min and labeled for 5 min. Cells were chased for the times indicated, lysed, and immunoprecipitated with antiinsulin and digested with PNGase F before SDS-PAGE. (B) Quantification by densitometry of the results shown in A. (C) The ICFP was expressed in a pep4-null strain. The cells were labeled and chased as in the legend to Fig. 2 B before insulin immunoprecipitation and digestion with PNGaseF followed by SDS-PAGE and fluorography. Note that in a sec18 strain intracellular ICFP persists, whereas in a pep4 strain intracellular insulin accumulates.