Molecular cloning studies have provided valuable structural informatio
n about the different subunits of cytoplasmic dynein and their relatio
nships to their axonemal dynein counterparts. Recent unexpected findin
gs regarding the role of this enzyme in mitosis have emerged from muta
tional analyses and microinjection experiments, while studies of organ
elle transport in vivo have revealed clues to mechanisms for physiolog
ical regulation of dynein activity.