RRC ID 29152
Author Saito-Nakano Y, Nakano A.
Title Sed4p functions as a positive regulator of Sar1p probably through inhibition of the GTPase activation by Sec23p.
Journal Genes Cells
Abstract BACKGROUND:Sar1p belongs to a unique subfamily of small GTPases and is essential for formation of the transport vesicles from the endoplasmic reticulum (ER) that are destined to the Golgi apparatus. To understand how the GTPase cycle of Sar1p is regulated, we screened for multicopy suppressors of sar1 ts mutants and identified SED4.
RESULTS:Although deletion of sed4 alone shows no growth defect, sar1 delta(sed4) double mutant cells are inviable. In the delta(sed4) background, the suppression activity of SAR1 towards sec12 and sec16 is lost. These observations suggest that SED4 is a very close partner of SAR1 and imply that Sed4p may act to increase the active Sar1p in the cell. Over-expression of SEC12 does not remedy the lethality of sar1 delta(sed4). The purified cytoplasmic domain of Sed4p does not show a guanine nucleotide exchange (GEF) activity toward Sar1p nor increase the GEF activity of Sec12p. On the contrary, over-expression of SED4 aggravates the ts growth of sec23 cells. The cytoplasmic domain of Sed4p weakly inhibits the GTPase-activating (GAP) activity of Sec23p toward Sar1p. In a microsome-based COPII binding assay, the binding of the GDP-form mutant Sar1p (D32G) is lower on the delta(sed4) microsomes than on the wild-type membranes.
CONCLUSION:We propose a model that Sed4p counteracts the GAP action of Sec23p on to Sar1p.
Volume 5(12)
Pages 1039-48
Published 2000-12-1
DOI 10.1046/j.1365-2443.2000.00391.x
PII gtc391
PMID 11168590
MeSH COP-Coated Vesicles Enzyme Activation Fungal Proteins / genetics Fungal Proteins / metabolism Fungal Proteins / physiology* GTP Phosphohydrolases / antagonists & inhibitors* GTP Phosphohydrolases / metabolism* GTPase-Activating Proteins / antagonists & inhibitors GTPase-Activating Proteins / metabolism Guanine Nucleotide Exchange Factors / metabolism Guanosine Triphosphate / metabolism Guanosine Triphosphate / physiology Membrane Proteins / genetics Membrane Proteins / metabolism Membrane Proteins / physiology* Models, Biological Monomeric GTP-Binding Proteins / genetics Monomeric GTP-Binding Proteins / metabolism* Saccharomyces cerevisiae / enzymology Saccharomyces cerevisiae / physiology* Saccharomyces cerevisiae Proteins* Vesicular Transport Proteins
IF 1.655
Times Cited 18
DNA material pRS316-SEC16 (RDB08769) pYS28-E52 (RDB08664) pYS6-7 (RDB08766) pYS6 (RDB08767) pYS25 (RDB08768) pSKY2-2 (RDB08770)