Rap activation is required for MTOC polarization towards anti-Ig-coated beads. Vector control and RapGAPII-expressing cells A20 cells that had been transfected with GFP-α-tubulin (green) were mixed with 3-μm diameter anti-IgG-coated fluorescent beads (blue). Time-lapse spinning disk confocal microscopy was used to acquire images every 60 s between 1 min and 16 min after adding the beads to the cells. The videos are played back at 5 frames per second (300X real time).