This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Dynactin is a multisubunit protein complex that works in conjunction with the microtubule-based motor, cytoplasmic dynein, to provide a wide range of subcellular localization and motile functions. Dynactin assists dynein by enhancing motor processivity and serving as an adaptor protein that allows dynein to interact with a variety of subcellular cargoes. To do this, dynactin relies on the distinct binding activities of different elements of its structure. The cargo-binding and dynein-binding domains allow dynactin to serve as a dynein adaptor, while processivity enhancement depends on the microtubule-binding and dynein-binding domains. All known cytoplasmic dynein-based transport requires dynactin's structural integrity. The dynactin subunit dynamitin (p50) acts as a molecular "glue" that anchors the dynein and microtubule-binding subunit of dynactin, p150(Glued), to the cargo-binding element. Within dynactin, dynamitin makes contacts with at least three other dynactin subunits as well as itself. This project is focused on obtaining new information on dynactin subunit organization, modification of dynactin subunits, and identifying proteins with which dynactin interacts in cells.