S-100 protein was examined for its ability to affect microtubule assembly—disassembly in vitro. Addition of S-100 protein inhibited microtubule assembly in a dose-dependent manner in the presence of Ca2+, but this effect was not observed in the presence of 2 mM EGTA. The interaction of microtubule proteins with S-100 protein was also demonstrated by Ca+-dependent affinity chromatography on S-100 protein—Sepharose. The proteins bound to the Sepharose column comigrated with tubulin as judged by sodium dodecyl sulfate—polyacrylamide gel electrophoresis. These results might suggest a possible physiological role of S-100 protein in the microtubule assembly—disassembly system.
