In mammalian cells, flat Golgi cisternae closely arrange together to form stacks. During mitosis, the stacked structure undergoes a continuous fragmentation process. The generated mitotic Golgi fragments are distributed into the daughter cells, where they are reassembled into new Golgi stacks. In this study, an in vitro assay has been developed using purified proteins and Golgi membranes to reconstitute the Golgi disassembly and reassembly processes. This technique provides a useful tool to delineate the mechanisms underlying the morphological change. There are two processes during Golgi disassembly: unstacking and vesiculation. Unstacking is mediated by two mitotic kinases, cdc2 and plk, which phosphorylate the Golgi stacking protein GRASP65 and thus disrupt the oligomer of this protein. Vesiculation is mediated by the COPI budding machinery ARF1 and the coatomer complex. When treated with a combination of purified kinases, ARF1 and coatomer, the Golgi membranes were completely fragmented into vesicles. After mitosis, there are also two processes in Golgi reassembly: formation of single cisternae by membrane fusion, and restacking. Cisternal membrane fusion requires two AAA ATPases, p97 and NSF (N-ethylmaleimide-sensitive fusion protein), each of which functions together with specific adaptor proteins. Restacking of the newly formed Golgi cisternae requires dephosphorylation of Golgi stacking proteins by the protein phosphatase PP2A. This systematic study revealed the minimal machinery that controls the mitotic Golgi disassembly and reassembly processes.The interphase Golgi apparatus, as seen by light or fluorescence microscopy, is a compact juxta-nuclear reticulum, located most often in the peri-centriolar region of the cell (1). Electron microscopy (EM) 2 shows that it is comprised of discrete Golgi stacks linked together by tubules that connect equivalent cisternae in adjacent stacks (2). At the onset of mitosis, the characteristic stacked organization of the Golgi apparatus undergoes extensive fragmentation (3, 4). The mitotic Golgi fragments generated by this disassembly process are subsequently distributed to daughter cells, where they are reassembled into new Golgi stacks after mitosis. So far, the mechanism that controls the Golgi disassembly and reassembly processes is not well understood.Biochemical reconstitution experiments have provided powerful tools with which to dissect biological processes. Two basic experimental approaches have been taken to reconstitute mitotic Golgi disassembly and reassembly. One involves semipermeabilized cells, in which cells are permeabilized gently with detergent (e.g. digitonin), washed with 1 M KCl to remove endogenous cytosol and peripheral membrane proteins, and then incubated in cytosol prepared from mitotic (or interphase) cells (5, 6). Cells can then be processed directly for immunofluorescence or electron microscopy, or biochemical analysis of proteins. This approach has been used to test the mitotic kinases that regulate the Golgi disassembly process (5, 6).The...