Localization of the tubulin binding site for tau protein.

Limited proteolysis of tubulin with subtilisin resulted in the removal of the carboxyl-terminal moiety of tubulin subunits. The remaining peptides from both alpha and beta tubulin lacking the carboxyl terminal did not bind to tau factor nor to MAP2 or MAP1. The carboxyl-terminal fragments bind to tau factor and MAP2 and both compete for the same binding sites in the tubulin molecule. Our results suggest that the carboxyl-terminal region of tubulin is a regulatory domain for the assembly of tubulin and the site for interaction with MAPs.