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

Brefeldin A (BFA) ~ (Hiirri et al., 1963) has been a frequently used transport inhibitor in mammalian cells. BFA was first reported to block the transport of vesicular stomatitis virus G protein (Takatsuki and Tamura, 1985) . Later it has been shown that BFA treatment results in the fusion of the Golgi membranes with the ER (Doms et al., 1989; Lippincott-Schwartz et al., 1989 , 1991a Strous et al., 1991) . The almost immediate effect of BFA is to detach at least two of the coat components-/3-COP ) and a 200-kD protein (Narula et al., 1992 )-from the Golgi stack, allowing Golgi membranes to form tubular extensions along microtubules that finally fuse with the ER . This effect of BFA has been proposed to reveal a normally occurring retrograde membrane traffic from the Golgi apparatus to the ER (Doms et al., 1989; Lippincott-Schwartz et al., 1989; Klausner et al., 1992) . BFA has also been reported to have effects on the organization of the endocytic compartment; TGN and endosomes form large tubular structures after a BFA treatment (Wood et al., 1991; Lippincott-Schwartz et al., 1991b; Reaves and Banting, 1992) .