Fig. 1. DRM-tagged wild-type spastin (wtSPG4) severs microtubules in COS-1 cells. Cos-1 cells seeded on glass coverslips were transfected with plasmids encoding the fusion proteins DRM-wtSPG4 or DRM-NK#1. After fixation, cells were immunolabeled with anti--tubulin monoclonal antibody and secondary antibody conjugated to Alexa Fluor-633. Images were collected with a LSM510 microscope equipped with a Plan-Apochromate 100x/1.4 oil DIC lens at scan-zoom set at `1', line average set at `4' and pinhole set to optical slice of 0.5 µm. The HeNe2 laser was used to visualize microtubules (a,d) and the HeNe1 laser was used to visualize the DRM-tagged constructs (b,e). The channel representing immuno-labeled microtubules was pseudo-colored in green. Most of microtubules are severed in the cells expressing DRM-wtSPG4 (a-c). The DRM-wtSPG4 fusion protein has a characteristic punctate distribution. Expression of the biologically inactive DRM-NK#1 construct leads to the decoration of intact microtubules by the fusion protein (d-f). Bar, 20 µm.