CHARACTERIZATION OF THE P22 SUBUNIT OF DYNACTIN REVEALS THE LOCALIZATION OF CYTOPLASMIC DYNEIN AND DYNACTIN TO THE MIDBODY OF DIVIDING CELLS

Dynactin, a multisubunit complex that binds to the microtubule motor c ytoplasmic dynein, may provide a link between dynein and its cargo. Ma ny subunits of dynactin have been characterized, elucidating the multi functional nature of this complex. Using a dynein affinity column, p22 , the smallest dynactin subunit, was isolated and microsequenced. The peptide sequences were used to clone a full-length human cDNA. Databas e searches with the predicted amino acid sequence of p22 indicate that this polypeptide is novel. We have characterized p22 as an integral c omponent of dynactin by biochemical and immunocytochemical methods. Af finity chromatography experiments indicate that p22 binds directly to the p150(Glued) subunit of dynactin. Immunocytochemistry with antibodi es to p22 demonstrates that this polypeptide localizes to punctate cyt oplasmic structures and to the centrosome during interphase, and to ki netochores and to spindle poles throughout mitosis. Antibodies to p22, as well as to other dynactin subunits, also revealed a novel localiza tion for dynactin to the cleavage furrow and to the midbodies of divid ing cells; cytoplasmic dynein was also localized to these structures. We therefore propose that dynein/dynactin complexes may have a novel f unction during cytokinesis.