Molecular motors are necessary for the motility of nuclear pores. (A) Nuclear pores and microtubule orientation in a growing yeast-like cell of U. maydis. NPCs are labeled by Nup133-GFP (N133), the cell edge is shown in blue, and the orientation of the microtubules is indicated by “+” and “−”. Note that the microtubule-organizing centers are located in the neck region between the growing bud and the mother cell (Fink and Steinberg, 2006). Images were subject to adjustment in brightness, contrast, and gamma settings. Bar is given in micrometers. (B) Bar chart showing NPC motility toward the bud (to MINUS) or toward the distal cell pole (to PLUS) in control cells (Control), null mutants of kinesin-1 (ΔKin1), and temperature-sensitive dynein mutants at restrictive temperature (Dyn2^ts). In control cells, NPC motility is a balanced process. Deleting the plus-motor kinesin-1 favors minus end–directed motility, whereas inactivation of the minus-motor dynein supports plus end–directed motion. Bars represent mean ± SEM of 3–6 experiments, covering 63–146 motility events in more than 50 nuclei. *, significant difference to wild-type at P < 0.05; ***, P < 0.0001. (C) Bar chart showing the relative number of nuclei with motility within 22 s observation time in control cells, kinesin-1 null mutants (ΔKin1), and conditional dynein mutants at restrictive conditions (Dyn2^ts). Bars represent mean ± SEM (n = 3 experiments; each bar corresponds to 103–169 nuclei in G2 phase and in S phase). *, significant difference to wild-type in G phase at P < 0.05; **, significant difference to wild-type in G phase at P < 0.001). (D) Localization of Nup133-labeled nuclear pores (yellow in overlay with the red nucleus, labeled with nuclear RFP, red) in control cells, kinesin-1 null mutants (ΔKin1), and temperature-sensitive dynein mutants (Dyn2^ts). Note that deletion of kinesin-1 or inactivation of dynein results in clustering of NPCs at the poles of the nucleus, which is most likely due to imbalanced NPC motility (see Fig. 4 B). Images were subject to adjustment in brightness, contrast, and gamma settings. Asterisks indicate the neck region where microtubules are nucleated. Bar represents micrometers. (E) Localization of Nup133-labeled nuclear pores (yellow in overlay with the red nucleus, labeled with nuclear RFP, red) in control cells, kinesin-1 null mutants (ΔKin1), and temperature-sensitive dynein mutants (Dyn2^ts). Microtubule orientation is indicated by “MINUS” and “PLUS”. Images were subject to adjustment in brightness, contrast, and gamma settings. Bar represents micrometers. (F) Colocalization of Nup107-mRFP (red, N107) and triple GFP-labeled dynein heavy chain (green, Dyn2). Dynein colocalizes with a NPC that moves toward the bud (see also Video 8). Images were subject to adjustment in brightness, contrast, and gamma settings. Time is given in seconds; bar represents micrometers. (G) Bar chart showing the relative number of nuclei with motility within 12 s observation time in control cells and kinesin-1/dynein double mutants at restrictive conditions (ΔKin1Dyn2↓). Bars are given as mean ± SEM of the mean of three experiments (>90 nuclei per bar) and an observation time of 22.5 s per nucleus. ***, significant difference to wild-type at P < 0.0001.