AN N-END RULE DESTABILIZATION MUTANT REVEALS PRE-GOLGI REQUIREMENTS FOR SEC7P IN YEAST MEMBRANE TRAFFIC

Sec7 protein (Sec7p) is required for membrane traffic in the yeast sec retory pathway. Because Sec7p regulates more than one stage in the pat hway, it has been difficult to assign the most proximal requirement fo r Sec7p action. We have engineered a novel mutant whose Sec7p levels a re regulated by growth conditions and by selective protein destabiliza tion according to the N-end rule. Sec7p depletion causes cell growth a rrest and accumulation of transport proteins with post; translational modifications indicative of Sec7p dependence for ER-to-Golgi traffic, in addition to the already characterized Gels requirements. Immuno-EM of sec7 revealed exaggeration of ER and Golgi membranes with protein a ccumulation in these exaggerated structures, suggesting that these reg ions may represent staging areas for cargo sorting and vesicle assembl y. (C) 1998 Academic Press.