Arf GTP-binding proteins and membrane traffic

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Arf GTP-binding proteins regulate membrane traffic, the formation of transport intermediates and the structure of organelles. Arf1 has been extensively studied, localizes to the Golgi complex and regulates membrane traffic between the endoplasmic reticulum and the Golgi complex. Arf6 is present at the plasma membrane and on endosomes and functions in the regulation of endosomal membrane traffic. One interest of the lab has been in the identification of sequences in Arf1 and Arf6 that specify localization and function. In order to map out sequences in Arf1 that specify Golgi localization, we made chimeras of Arf1 and Arf6 and expressed these chimeric Arfs in cells to see whether they could associate with the Golgi complex. We identified a sixteen amino acid sequence in Arf1 that when inserted into Arf6 allowed it to associate with the Golgi. We found that those sequences in Arf1 allows Arf1-GDP to be recruited to the early part of the Golgi by binding to membrin, a Golgi-associated protein implicated in membrane fusion (Honda et al., 2005). Arf1 lacking those sequences could only associate with the late Golgi. These studies revealed the varied and distinct interactions that Arf1 has with the Golgi complex, reflecting different regulatory molecules on the early and late aspects of the Golgi.