Efficient export of the glucose transporter Hxt1p from the endoplasmic reticulum requires Gsf2p

Mutations in the GSF2 gene cause glucose starvation phenotypes in Saccharom yces cerevisiae. me have isolated the HXT1 gene, which encodes a low affini ty, high-capacity glucose transporter, as a multicopy suppressor of a gsf2 mutation. We show that gsf2 mutants accumulate Hxt1p in the endoplasmic ret iculum (ER) and that Gsf2p is a 46-kDa integral membrane protein localized to the ER. gsf2 mutants also display a galactose growth defect and abnormal localization of the galactose transporter Gal2p but are not defective in f unction or localization of the high-affinity glucose transporter Hxt2p. The se findings suggest that Gsf2p functions in the ER to promote the secretion of certain hexose transporters.