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Abstract

The small GTPase Arf1p is involved in a number of different cellular processes. Currently best understood is the role of Arf1p in COPI vesicle generation at different levels of the Golgi apparatus. Furthermore, mounting evidence suggests that Arf1p plays a role in cargo recruitment probably in concert with cargo receptors. Yet, thus far uncharacterized trafficking pathway, especially from the trans-Golgi, are likely to require ARF1 function. To identify new interactors and effectors of Arf1p and to unravel new transport pathways, we performed a differential affinity chromatography. Chs5p and Bch1p, a member of the Bud7p-Chs6p family, both specifically bound to the activated form of Arf1p. We showed that all members of the Bud7p-Chs6p family physically interact with Arf1p and Chs5p. Moreover, the Bud7p-Chs6p family proteins interact with each other and form higher molecular weight complexes. In addition they are all at least partially localized to the trans Golgi. Most importantly, at least Bud7p and Bch2p are found on vesicles generated from Golgi membranes in vitro. Finally, we propose that the Bud7p-Chs6p family proteins act as cargo receptors and are involved in Arf1p-dependent post-Golgi transport steps of cargo molecules.