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J. Biol. Chem., Vol. 277, Issue 52, 50355-50364, December 27, 2002
From the Department of Biochemistry and Molecular Biology, St.
Louis University School of Medicine, St. Louis, Missouri 63104
The cisternal maturation model proposes that
secretory proteins transit the Golgi in cisternae that mature by the
continuous retrograde transport of Golgi enzymes in vesicles. We have
tested the hypothesis that de novo generation of transport
intermediates containing medial, trans, and trans Golgi network
(TGN) enzymes is reconstituted in vitro. Our
analysis shows that the majority of transport is mediated by a steady
state of transport intermediate production and consumption by Golgi
cisternae, with only a minor contribution of pre-existing transport
intermediates. Transport in the medial and trans regions of the stack
involved intermediates containing Golgi enzymes, apparently moving in a
retrograde direction. In contrast, transport between the trans Golgi
and TGN was exclusively mediated by intermediates containing secretory
protein, as expected for anterograde transport. These intermediates may
be physiologically relevant, because only these two specific types of
intermediates can be detected in cell homogenates. By analogy to
the coatomer (COPI)-independent transport of Golgi enzymes to
the endoplasmic reticulum, the steady-state production of intra-Golgi
transport intermediates was not impaired by inhibition of COPI vesicle
formation. These data suggest a model for COPI-independent intra-Golgi
transport by cisternal maturation with a shift in mechanism to
anterograde transport at the trans Golgi and TGN boundary.
Present address: Department of Cell Biology and Neuroscience,
University of California, Riverside, CA 92521.
§
To whom correspondence should be addressed: Dept. of Biochemistry
and Molecular Biology, St. Louis University School of Medicine, 1402 South Grand Blvd., M173, St. Louis, MO 63104. Tel.: 314-577-8179; Fax:
314-577-8156; E-mail: weidmanp@slu.edu.
Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc. This article has been cited by other articles:
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