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

To obtain a more detailed picture of the effect of caffeine and reduced temperature on the membranes operating between the ER and the Golgi complex, it is necessary to study whether the distribution of other markers for these membranes such as p53 (Schweizer et al., 1988) , Corona virus E1 glycoprotein (Machamer et al., 1990) , and rab2 (Chavrier et al., 1990) , is also affected. Caffeine at reduced temperature on the one hand inhibited the exit of proteins from the ER and on the other hand induced a selective translocation of pre-and cis-Golgi membranes to peripheral locations; this is in contrast to the BFA action which seems to translocate unselectively all Golgi membranes from their normal perinuclear location (Lippincott-Schwartz et al., 1989 , 1991a Doms et al., 1989; Fujiwara et al., 1988; Strous et al., 1991) . Further, caffeine did not detach H-COP from the Golgi membranes nor did it translocate man II to the ER. Thus, the effect of caffeine on the organization of the membranes between the ER and the Golgi complex is clearly different from that induced by BFA. The different effect of BFA and caffeine on the Golgi complex would indicate that the Golgi complex is composed of two subsets of homotypic membranes differentially sensitive to caffeine treatment. Whether this is also reflected in the differences of the coat structures of these membranes remains to be seen.