Effect of caffeine and reduced temperature (20 degrees C) on the organization of the pre-Golgi and the Golgi stack membranes

BHK-21 cells were infected with SFV ts-1, shifted to the restrictive temperature, labeled at 3 h 45 min after infection with [35S]methionine for 10 min and chased for 3 h at 20, 21, 22, 23, 24, 25, 26, and 28~ with or without 10 mM caffeine. E1 glycoproteins were then immunoprecipitated and analyzed for their sensitivity to Endo H. In the presence of 10 mM caffeine, SFV El-glycoproteins remained Endo H sensitive up to 24~ (Fig. 1 a) . At 25~ and at higher temperatures E1 reached the Golgi stack as indicated by the increasing amount of Endo H-resistant form of E1 ( Fig. 1 a) . In control cells ( Fig. 1 b) , E1 reached the Golgi stack already at 20~ as indicated by the maturation of the proteins to the Endo H-resistant form. In Fig. 1 b, it can be seen that E1 does not become completely resistant to Endo H treatment even at 28~ This, however, is a constant finding for SFV ts-1 and has been reported and discussed earlier (Saraste and Kuismanen, 1984; Gahmberg et al., 1986) .