Nuclear pore motility is dependent on microtubules. (A) Graph showing trajectories of nuclear pore motility within a nucleus, observed over 17.2 s. Note that all NPCs within the field of observation were included. NPCs move along a single track, suggesting that one or few cytoskeletal fibers underlie this motility. (B) Colocalization of microtubules (labeled with GFP-α-tubulin, Tub1) and a nuclear reporter (nlsRFP). Images were subject to adjustment in brightness, contrast, and gamma settings. Note that microtubules are in proximity with the nucleus. Bar represents micrometers. (C) Image series showing motility of a NPC (green, N107) along a mRFP-α-tubulin (red, Tub1) labeled microtubule (arrowhead). Images were subject to adjustment in brightness, contrast, and gamma settings. Time is given in seconds; bar represents micrometers. See also Video 7. (D) Bar chart showing the effect of cytoskeleton disrupting drugs on NPC motility. DMSO: the solvent dimethyl sulfoxide; Ben: the microtubule inhibitor benomyl; LatA: the F-actin inhibitor latrunculin A. **, P < 0.01. Bars represent mean ± SEM of three experiments and >130 analyzed nuclei. (E) Image series showing NPC motility into a photobleached area of the nucleus. In control cells (DMSO) NPCs rapidly migrate into the bleached zone (indicated by circle). This motility was not seen after 30 min incubation with the microtubule inhibitor (Benomyl). Images were subject to adjustment in brightness, contrast, and gamma settings. Time is given in seconds; bar represents micrometers. Contrast was inverted. (F) Graph showing recovery of average fluorescence intensity after photobleaching with a 405-nm laser pulse. DMSO: the solvent dimethyl sulfoxide; Ben: the microtubule inhibitor benomyl. Each data point represents mean ± SEM (n = 10). Note that transient pairing and clustering of NPCs made the measurement of pore numbers inaccurate; therefore, the recovery of the average intensity of Nup107-GFP fluorescence is given.