Immunofluorescence localization of proteins of high molecular weight along intracellular microtubules

To help clarify the role, in cytoplasmic microtubule function, of the proteins of high molecular weight that coassemble with tubulin in vitro, a monospecific antibody against the proteins of high molecular weight was prepared from the serum of immunized rabbits by affinity chromatography. With indirect immunofluorescence we found that the protein in both cultured neuroblastoma cells and 3T3 cells in distributed in an extensive filamentous array that originates at sites near the nucleus and extends to the cell periphery or, in neuroblastoma cells, gathers into bundles which enter neurites. No filaments were seen with nonspecific antibodies from serum taken before immunization, and prior incubation of the specific antibody with purified protein of high molecular weight (but not tubulin) prevented filament visualization. The filamentous pattern in 3T3 cells was disrupted by colchicine. This evidence indicates that the proteins of high molecular weight are found in cells in association with cytoplasmic microtubules.