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Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
Cytoplasmic dynein is a microtubule minus-end-directed motor that is thought to power the transport of vesicles from the TGN to the apical cortex in
polarized epithelial cells. Trans-Golgi enriched membranes, which were isolated from primary polarized intestinal epithelial cells, contain both the actin-based
motor myosin-I and dynein, whereas isolated Golgi
stacks lack dynein but contain myosin-I (Fath, K.R.,
G.M. Trimbur, and D.R. Burgess. 1994. J. Cell Biol.
126:661-675). We show now that Golgi stacks in vitro
bind dynein supplied from cytosol in the absence of
ATP, and bud small membranes when incubated with
cytosol and ATP. Cytosolic dynein binds to regions of
stacks that are destined to bud because dynein is
present in budded membranes, but absent from stacks after budding. Budded membranes move exclusively
towards microtubule minus-ends in in vitro motility assays. Extraction studies suggest that dynein binds to a
Golgi peripheral membrane protein(s) that resists extraction by ice-cold Triton X-100. In the presence of cytosol, these membrane ghosts can move towards the minus-ends of microtubules. Detergent-extracted Golgi
stacks and TGN-containing membranes are closely associated with an amorphous matrix composed in part of
spectrin and ankyrin. Although spectrin has been proposed to help link dynein to organellar membranes, we
found that functional dynein may bind to extracted
membranes independently of spectrin and ankyrin.
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