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.