APEX2 labeling resolves flagellum subdomains. (A and B) AC1-APEX2 cells were fixed and examined by fluorescence microscopy after staining with anti-PFR antibody (Alexa 488, green), streptavidin (Alexa 594, red), and DAPI (blue). Boxes show zoomed in version of the cells. Brackets point out streptavidin (Alexa 594, red) at the flagellum tip. (C and D) FS179-APEX2 cells were examined by immunofluorescence with anti-PFR antibody (Alexa 488, green), streptavidin (Alexa 594, red) and DAPI (blue). White brackets indicate the distal region of the flagellum that is not labeled by streptavidin. Boxes show zoomed in versions of the cells. Brackets indicate that streptavidin (Alexa 594, red) is excluded from the flagellum tip. Scale bar, 5 μm. (E) Scheme used to identify biotinylated proteins from the indicated cell lines (29-13, AC1-APEX2, and FS179-APEX2).