THE P150(GLUED) COMPONENT OF THE DYNACTIN COMPLEX BINDS TO BOTH MICROTUBULES AND THE ACTIN-RELATED PROTEIN CENTRACTIN (ARP-1)

p150(Glued) was first identified as a polypeptide that copurifies with cytoplasmic dynein, the minus-end-directed microtubule-based motor pr otein, and has more recently been shown to be present as a member of t he oligomeric dynactin complex, which includes the actin-related prote in centractin (Arp-l), Dynactin is thought to mediate dynein-driven ve sicle motility, as well as nuclear transport, in lower eukaryotes, The mechanism by which dynactin may function in these cellular processes is unknown, To examine the role of the dynactin complex in vivo, we ov erexpressed the rat cDNA encoding p150(Glued) in Rat-2 fibroblasts. Ov erexpression of full-length, as well as C-terminal deletion, construct s resulted in the decoration of microtubules with the p150(Glued) poly peptides. This cellular evidence for microtubule association was corro borated by in vitro microtubule-binding assays. Amino acids 39-150 of p150(Glued) were determined to be sufficient for microtubule associati on. We also tested for a direct interaction between p150(Glued) and ce ntractin, In vitro translated centractin was specifically retained by a p150(Glued) affinity column, and this interaction was blocked by a s ynthetic peptide which corresponds to a highly conserved moth from the C terminus of p150(Glued). These results demonstrate that p150(Glued) , a protein implicated in cytoplasmic dynein-based microtubule motilit y, is capable of direct binding to both microtubules and centractin.