The Sar1 GTPase coordinates biosynthetic cargo selection with endoplasmic reticulum export site assembly.
Cargo selection and export from the endoplasmic reticulum is mediated by the COPII coat machinery that includes the small GTPase Sar1 and the Sec23/24 and Sec13/31 complexes. We have analyzed the sequential events regulated by purified Sar1 and COPII coat complexes during synchronized export of cargo from the ER in vitro. We find that activation of Sar1 alone, in the absence of other cytosolic components, leads to the formation of ER-derived tubular domains that resemble ER transitional elements that initiate cargo selection. These Sar1-generated tubular domains were shown to be transient, functional intermediates in ER to Golgi transport in vitro. By following cargo export in live cells, we show that ER export in vivo is also characterized by the formation of dynamic tubular structures. Our results demonstrate an unanticipated and novel role for Sar1 in linking cargo selection with ER morphogenesis through the generation of transitional tubular ER export sites.
Aridor
M
M
Department of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Fish
K N
KN
Bannykh
S
S
Weissman
J
J
Roberts
T H
TH
Lippincott-Schwartz
J
J
Balch
W E
WE
D000818:Animals; D001692:Biological Transport; D022181:COP-Coated Vesicles / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004789:Enzyme Activation; D005453:Fluorescence; D006056:Golgi Apparatus / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008562:Membrane Glycoproteins; D018715:Microscopy, Video; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013997:Time Factors; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins / Q000378:metabolism
C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae