Evidence for cooperative interactions between the two motor domains of cytoplasmic dynein

Cytoplasmic dynein is a force-transducing ATPase that powers the movement o f cellular cargoes along microtubules. Two identical heavy chain polypeptid es (> 500 kDa) of the cytoplasmic dynein complex contain motor domains that possess the ATPase and microtubule-binding activities required for force p roduction [1]. It is of great interest to determine whether both heavy chai ns (DHCs) in the dynein complex are required for progression of the mechano chemical cycle and motility, as observed for other dimeric motors. We have used transgenic constructs to investigate cooperative interactions between the two motor domains of the Drosophila cytoplasmic dynein complex. We show that 138 kDa and 180 kDa amino-terminal fragments of DHC can assemble with full-length DHC to form heterodimeric complexes containing only a single m otor domain. The single-headed dynein complexes can bind and hydrolyze ATP, yet do not show the ATP-induced detachment from microtubules that is chara cteristic of wild-type homodimeric dynein. These results suggest that coope rative interactions between the monomeric units of the dimer are required f or efficient ATP-induced detachment of dynein and unidirectional movement a long the microtubule.