Analyzing the components of microtubules: antibodies against chartins, associated proteins from cultured cells.

In previous work, we have identified cytoplasmic microtubule-associated proteins by isolating the microtubule organelles of several different cultured cells. Among those proteins are the chartins, a family of polypeptides with related sequence but of varying molecular weight and isoelectric point. Biochemical analyses of the distribution of the chartins in the cytoplasm, and among cells with different functions, suggest that they may regulate microtubule structure in vivo. We describe here the preparation and application of antibodies to chartins. These antibodies enable us to demonstrate that the chartins colocalize with assembled tubulin in the cytoplasm, as assessed by immunofluorescence, so that they fulfill a major criterion that has been applied to other putative microtubule components. The results also demonstrate that the tau proteins, which fractionate and copurify with chartins, are in fact clearly distinguishable from them. The implications of these results for evaluating microtubule composition are discussed.