It has been previously demonstrated that both cytoplasmic microtubules and the microtubules of cilia, flagella, and sperm tail contain tubulin. Although the morphology of cytoplasmic microtubules and that of axonemes differs in cells from which they have been isolated, the tubulin of the two structures shares physical and chemical properties. In some mammalian tissues, such as tracheal epithelium, cilia and basal bodies are difficult to isolate and characterize. The use of an enzyme-labeled immunoglobulin probe would facilitate identification and in situ localization of such proteins. Tubulin prepared from porcine brain by ion-exchange chromatography and from rat brain by the method of cyclic polymerization and depolymerization with subsequent disk gel electrophoresis with SDS were injected intravenously into rabbits. The animals were intermittently bled and the antisera extracted. The specificity of the antisera was proved by indirect immunofluorescence staining of the mitotic spindle, specific blocking of spindle staining by purified tubulin and not by other proteins, staining of 3T3 cytoplasmic microtubules, single line on immunoelectrophoresis, failure of control antisera to show any of these, and precipitation of antibody with all tubulin preparations and not with actin. We have shown by electron microscopy of ciliated cells of the tracheal epithelium stained with antitubulin by the indirect enzyme-labeled antibody method that the basal bodies, outer doublets, and central pair of the cilia contain tubulin. This indicates that tubulin in microtubules of cilia and basal bodies of rat tracheal epithelium is antigenically similar to tubulin extracted from cytoplasmic neurotubules of brains from the same species and from a different mammalian species. No other axonemal structures stained with the antitubulin. Three different preparations of tubulin from pigs and rats were used to immunize rabbits. All elicited similar antisera which gave identical staining patterns. The specificity of the staining was demonstrated by the absence of staining with immune serum absorbed with purified tubulin, the absence of staining with preimmune serum, and the absence of staining if any of the reagents were omitted during the staining reaction.

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