Anterograde flow of cargo across the golgi stack potentially mediated via bidirectional "percolating" COPI vesicles.
How do secretory proteins and other cargo targeted to post-Golgi locations traverse the Golgi stack? We report immunoelectron microscopy experiments establishing that a Golgi-restricted SNARE, GOS 28, is present in the same population of COPI vesicles as anterograde cargo marked by vesicular stomatitis virus glycoprotein, but is excluded from the COPI vesicles containing retrograde-targeted cargo (marked by KDEL receptor). We also report that GOS 28 and its partnering t-SNARE heavy chain, syntaxin 5, reside together in every cisterna of the stack. Taken together, these data raise the possibility that the anterograde cargo-laden COPI vesicles, retained locally by means of tethers, are inherently capable of fusing with neighboring cisternae on either side. If so, quanta of exported proteins would transit the stack in GOS 28-COPI vesicles via a bidirectional random walk, entering at the cis face and leaving at the trans face and percolating up and down the stack in between. Percolating vesicles carrying both post-Golgi cargo and Golgi residents up and down the stack would reconcile disparate observations on Golgi transport in cells and in cell-free systems.
Orci
L
L
Department of Morphology, University of Geneva Medical School, 1 rue Michel Servet, 1211 Geneva 4, Switzerland.
Ravazzola
M
M
Volchuk
A
A
Engel
T
T
Gmachl
M
M
Amherdt
M
M
Perrelet
A
A
Sollner
T H
TH
Rothman
J E
JE
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D016466:CHO Cells; D002451:Cell Compartmentation; D006224:Cricetinae; D017931:DNA Primers; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D013347:Subcellular Fractions / Q000378:metabolism
D017931:DNA Primers