Ultrastructural localization of tubulin in cultured fibroblasts.

Antibodies to barin tubulin were created in rabbits and used to localize tubulin in cultured fibroblasts. Cells were fixed and permeabilized using the EGS procedure (Willingham et al: J Cell Biol 79:256a, 1978). Tubulin was localized and quantified using a ferritin-bridge labeling method. Antibody localization was generally confined to morphologically identifiable microtubules, with a smaller concentration in a diffuse cytoplasmic distribution. Following treatment with colchicine, morphologically identifiable microtubules disappeared and the amount of diffuse localization in the cytosol increased. However, a significant concentration of tubulin was found associated with the microfilament mat under the plasma membrane after colchicine treatment, whereas in untreated cells, very little tubulin was found in the microfilament mat. These results demonstrate that tubulin is a component of microtubules and that colchicine treatment results in an association of this tubulin with microfilaments.