Sentin is a microtubule plus end–tracking protein. (A) GFP-Sentin (green) colocalized with EB1-mCherry (red) at the growing microtubule plus ends. The area boxed in white is magnified and placed at the bottom right. Also see Video 3. (B) The microtubule plus end localization of Sentin was revealed using a polyclonal anti-Sentin antibody. (C) Cells expressing GFP-Sentin were fixed and stained with microtubules. Microtubule tip localization was detected for 75% of the microtubules in the control cells (n = 5), whereas only 28% were observed after EB1 RNAi (n = 9). (D) A series of Sentin truncations revealed that the C-terminal region is essential and sufficient for plus end tracking. Frequency (percentage) of tip localization on growing microtubules for each Sentin fragment is presented (>50 microtubules analyzed). GFP images are shown on the right. Bars: (A and D) 10 µm; (B and C) 5 µm.