Anti-GRASP55 antibody and full-length GRASP55 inhibits mitosis-specific Golgi fragmentation in permeabilized cells. An in vitro assay reconstituting Golgi fragmentation by mitotic cytosol described previously (Acharya et al., 1998), was incubated with affinity purified preimmune IgG, anti-GRASP55 antibody, or purified recombinant GRASP55. Cells were fixed and processed for immunofluorescence microscopy by using an anti-giantin or anti-mannosidase II antibody to determine the percentage of cells with fragmented Golgi membranes. The data represents the average of individual experiments (buffer, n = 12; preimmune, n = 4; anti-GRASP55, n = 4; recombinant GRASP55, n = 4).