AbstractPolyclonal antibodies have been raised against the peptide 28–38 of the β‐subunit of the tubulin heterodimer in order to study the accessibility of this region in the tubulin heterodimer and in various tubulin assemblies. These antibodies were specific for all β'‐tubulin subunits, except for β‐tubulin isotypes, and did not recognize the α‐tubulin subunit. The 28–38 region does not play a role in the interaction between the α‐and β‐subunits since it was accessible to the antibodies on the native heterodimer. The accessibility of the antibodies was not modified by several microtubular poisons. In contrast, in all tubulin assemblies obtained in the presence of microtubule associated proteins, the region 28–38 was not available to the antibodies. These antibodies did not react with microtubules or tubulin spirals assembled either from microtubule proteins or from pure tubulin when these tubulin assemblies were probed in the absence of free tubulin after centrifugation on glass coverslips. In addition, antibodies failed to interact with the microtubule cytoskeleton in cultured Ptk2 cells indicating that the 28–38 region of β‐tubulin is also protected in cellular structures. These observations suggest that the 28–38 region of the β‐tubulin subunit is either located in a zone of interaction between two successive tubulin dimers within a protofilament or hidden by an allosteric conformational change which occurs during tubulin
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