Evidence for actin-dependent organelle movement was first obtained fro
m studies of cytoplasmic streaming in plants. These studies, together
with cell-free organelle motility studies and biophysical analyses of
muscle myosin, support a model whereby organelle-associated motor mole
cules utilize the energy of adenosine triphosphate binding and hydroly
sis to drive movement along F-actin tracks. Recent studies indicate th
at this mechanism for organelle movement may be responsible for organe
lle and vesicle movement during secretion, endocytosis and mitochondri
al inheritance in a variety of eukaryotes.