Calmodulin-microtubule association in cultured mammalian cells.

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Abstract
A Triton X-100 lysed cell system was used to identify calmodulin on the cytoskeleton of 3T3 and transformed SV3T3 cells. By indirect immunofluorescence, calmodulin was found to be associated with both the cytoplasmic microtubule complex and the centrosomes. A number of cytoplasmic microtubules more resistant to disassembly upon either cold (0-4.degree. C) or hypotonic treatment, as well as following dilution were identified. Most of the stable microtubules appeared to be associated with the centrosome at 1 end and with the plasma membrane at the other end. These microtubules could be induced to depolymerize by .mu.M Ca2+ concentrations. By interacting directly with the microtubule, calmodulin may influence microtubule assembly and ensure the Ca2+-sensitivity of both mitotic and cytoplasmic microtubules.