BUNDLING OF MICROTUBULES IN TRANSFECTED CELLS DOES NOT INVOLVE AN AUTONOMOUS DIMERIZATION SITE ON THE MAP2 MOLECULE

We have searched for putative dimerization sites in microtubule-associ ated protein 2 (MAP2) that may be involved in the bundling of microtub ules. An overlapping series of fragments of the embryonic form MAP2c w ere created and immunologically ''tagged'' with an 11 amino acid seque nce from human c-myc. Nonneuronal cells were transfected simultaneousl y with one of these myc-tagged fragments and with full-length native M AP2c. Immunolabeling with site-specific antibodies allowed the two tra nsgene products to be located independently within the cytoplasm of a single double-transfected cell. All transfected cells contained bundle d microtubules to which the full-length native MAP2 was bound. The dis tribution of the tagged MAP2 fragment relative to these MAP2-induced b undles was determined by the anti-myc staining. None of the fragments tested, representing all of the MAP2c sequence in overlapping pieces, were associated with MAP2-induced microtubule bundles. These results s uggest that MAP2-induced bundle formation in cells does not involve an autonomous dimerization site within the MAP2 sequence.