A MICROTUBULE-INTERACTING PROTEIN INVOLVED IN COALIGNMENT OF VIMENTININTERMEDIATE FILAMENTS WITH MICROTUBULES

A protein of M(r) 210 000 was identified in 3T3 cells by immunoblottin g and by immunoprecipitation with a monoclonal antibody MA-01. The pro tein was thermolabile and was located on 3T3 microtubules prepared by taxol-driven polymerization in vitro. On fixed cells the MA-01 antigen was located on interphase and mitotic microtubular structures, vinbla stine paracrystals, taxol bundles and colcemid-resistant microtubules. Microinjection experiments with purified MA-01 antibody followed by d ouble immunofluorescence have shown that the injection of antibody led to disruption of vimentin filaments, whereas the distribution of cyto plasmic microtubules was unchanged. The collapse of vimentin filaments started 30 minutes after injecting the antibody at immunoglobulin con centrations 2 mg ml(-1) or higher and reached its maximum 3-6 hours af ter the injection. Within 20 hours after the injection vimentin filame nts became reconstituted. Microinjection of the antibody into cells pr e-treated with vinblastine resulted in localization of the MA-01 antig en on vinblastine paracrystals as well as on coiled vimentin filaments . The data presented suggest that the MA-01 antigen is a new microtubu le-interacting protein that mediates, directly or indirectly, an inter action between microtubules and vimentin intermediate filaments.