BETA-TUBULIN FOLDING IS MODULATED BY THE ISOTYPE-SPECIFIC CARBOXY-TERMINAL DOMAIN

To investigate the contribution of the carboxy-terminal domain in the process of tubulin folding anal dimer formation, we constructed a beta (1)-beta(3) tubulin chimaera and two truncated carboxy-terminal beta(3 )-tubulins. The capacity of these altered polypeptides to incorporate into dimers and into microtubules was tested by non-denaturing electro phoresis and co-assembly experiments. The chimaera and the truncated p rotein with a deletion encompassing the last 12 amino acid residues (b eta(3) Delta C12) were incorporated into dimers and microtubules, thou gh the level of incorporation was diminished compared to wild-type bet a(3)-tubulin. However, the level of incorporation of beta(3) Delta C12 into subtilisin-digested dimers tvas similar to the incorporation of wild-type beta(3)-tubulin. Since subtilisin deletes the carboxy-termin al region, these results suggest a regulatory role of the carboxyl-ter minal region in the folding process itself and not in the formation of the dimer.