Cytoplasmic dynein is a minus end-directed motor for membranous organelles

The role of cytoplasmic dynein in microtubule-based organelle transport was examined using a reconstituted assay developed from chick embryo fibroblasts. Factors present in a high-speed cytosol caused the movement of purified organelles on microtubules predominantly in the minus end direction. Inactivation of cytoplasmic dynein in the high-speed cytosol by vanadate-mediated UV photocleavage inhibited minus end-directed organelle motility by over 90%. Addition of purified cytoplasmic dynein to the inactive cytosol restored minus end-directed organelle motility, although purified cytoplasmic dynein by itself did not support organelle movement. We propose that cytoplasmic dynein is the motor for minus end-directed organelle movement, but that additional cytosolic factors are also required to produce organelle motility.