Yos 1 p is a Novel Subunit of the Yip 1 p-Yif 1 p Complex and is Required for Transport Between the ER and the Golgi complex

Yeast Yip1p is a member of a conserved family of transmembrane proteins that interact with Rab GTPases. Previous studies have also indicated a role for Yip1p in the biogenesis of ER-derived COPII transport vesicles. In this report we describe the identification and characterization of the uncharacterized open reading frame YER074W-A as a novel multi-copy suppressor of the thermosensitive yip1-4 strain. We have termed this gene YOS1 (Yip One Suppressor 1). Yos1p is essential for growth and for function of the secretory pathway; depletion or inactivation of Yos1p blocks transport between the ER and the Golgi complex. YOS1 encodes an integral membrane protein of 87 amino acids that is conserved in eukaryotes. Yos1p localizes to ER and Golgi membranes and is efficiently packaged into ER-derived COPII transport vesicles. Yos1p associates with Yip1p and Yif1p, indicating Yos1p is a novel subunit of the Yip1p-Yif1p complex.