Preculturing HeLa-DynDN clones in the absence of tet induces overexpression of DN dynamin and a block in Tfn-FITC endocytosis. HeLa-DynWT or DN cells were precultured in the presence of tet (+tet) to suppress expression from the transfected dynamin cDNA, or in the absence of tet (–tet) to induce it. (A) Immunoblot of cell lysates to detect dynamin. (B) Cells were incubated with Tfn-FITC at 37° C for up to 1 hour. Relative mean fluorescence intensity of viable cells was determined by flow cytometry. The mean ± SD of 4 independent experiments is shown (**.001 < P < .01).