Centractin is an actin-related protein that shares 53% homology with conventional actin and has a similar nucleotide binding core. Biochemical studies show that centractin in a member of a stable, polypeptide complex named dynactin, which itself has been implicated in activating dynein mediated vesicle transport along microtubules. We are using transient transfection assays to investigate the effects of overexpressing centractin in PtK2 cells, studying the result by confocal fluorescent immunomicroscopy using antibodies to centractin and other cytoskeletal proteins plus fluorescent phalloidin for filamentous actin. Two distinct patterns of centractin localization are consistently observed; filamentous centractin located throughout the cytoplasm, and perinuclear accumulations. The latter are curved and highly three-dimensional. To further explore the nature of the perinuclear accumulations, we applied our methods for sequential confocal fluorescence and IVEM of the same cell preparations. The result is that the perinuclear fluorescence co-localizes with an apparently membranous structure near the nucleus that has the morphology of the Golgi apparatus. 8-31-96
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