Regulation of Nuclear Envelope Assembly and Disassembly by ARF and other GTP-Binding Proteins

At the onset of mitosis in higher eukaryotes the nuclear envelope, ER, and Golgi complex are partially or completely converted to small vesicles. After mitosis, these biochemically distinct vesicles must fuse selectively to reassemble each organelle. The potential similarities between this process and the process of vesicular transport through the secretory pathway were pointed out by Warren (1985). Secretion involves the regulated formation of coated vesicles at one compartment and their fusion with a specific target membrane (Rothman and Orci, 1992). Secretion ceases during mitosis (Hesketh et al., 1984; Colman et al., 1985), indicating that vesicle formation and/or vesicle fusion are temporarily inhibited. Warren suggested that a mitotic block to vesicle fusion would be sufficient to cause organelles to vesiculate. Newport and Spann (1987) showed that mitotic disassembly of nuclear membranes required an unknown stoichiometric factor (s), perhaps coat proteins. However, direct evidence for the mechanism of mitotic disassembly of the nuclear envelope, or its relationship to membrane traffic, was lacking.