Sec16 is a determinant of transitional ER organization.
BACKGROUND
Proteins are exported from the ER at transitional ER (tER) sites, which produce COPII vesicles. However, little is known about how COPII components are concentrated at tER sites. The budding yeast Pichia pastoris contains discrete tER sites and is, therefore, an ideal system for studying tER organization.


RESULTS
We show that the integrity of tER sites in P. pastoris requires the peripheral membrane protein Sec16. P. pastoris Sec16 is an order of magnitude less abundant than a COPII-coat protein at tER sites and seems to show a saturable association with these sites. A temperature-sensitive mutation in Sec16 causes tER fragmentation at elevated temperature. This effect is specific because when COPII assembly is inhibited with a dominant-negative form of the Sar1 GTPase, tER sites remain intact. The tER fragmentation in the sec16 mutant is accompanied by disruption of Golgi stacks.


CONCLUSIONS
Our data suggest that Sec16 helps to organize patches of COPII-coat proteins into clusters that represent tER sites. The Golgi disruption that occurs in the sec16 mutant provides evidence that Golgi structure in budding yeasts depends on tER organization.
Connerly
Pamela L
PL
Department of Molecular Genetics and Cell Biology, The University of Chicago, 920 East 58th Street, Chicago, Illinois 60615, USA.
Esaki
Masatoshi
M
Montegna
Elisabeth A
EA
Strongin
Daniel E
DE
Levi
Stephanie
S
Soderholm
Jon
J
Glick
Benjamin S
BS
D000595:Amino Acid Sequence; D022181:COP-Coated Vesicles / Q000378:metabolism*; D019295:Computational Biology; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000502:physiology; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D015151:Immunoblotting; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D028861:Nuclear Pore Complex Proteins; D010843:Pichia; D021381:Protein Transport / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013696:Temperature
D008565:Membrane Proteins; D028861:Nuclear Pore Complex Proteins; C079620:SEC13 protein, S cerevisiae; C096367:SEC16 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins