Yeast ER-Golgi v-SNAREs Bos1p and Bet1p differ in steady-state localization and targeting

Vesicle specific SNAP receptors (V-SNAREs) Bos1p and Bet1p are involved in targeting of anterograde vesicles between the endoplasmic reticulum (ER) an d early Golgi of Saccharomyces cerevisiae, To analyze factors that influenc e the targeting of these proteins, alpha-factor tagged versions of Bos1p an d Bet1p were employed. The alpha-factor can be cleaved off by the Kex2p pro tease as soon as the hybrid proteins reach the late Golgi compartment. The data obtained by monitoring of Kex2p cleavage, by immunofluorescence micros copy and cell fractionation showed that Bos1-alpha and Bet1-alpha have diff erent cellular localization and dynamics. Bos1-alpha is an ER protein, whic h recycles between the Golgi and the ER in COPI-dependent manner. Bet1-alph a is an early Golgi protein and it does not change its localization under c onditions when other recycling Golgi proteins can be trapped in the ER.