Brefeldin A acts to stabilize an abortive ARF-GDP-Sec7 domain protein complex: Involvement of specific residues of the Sec7 domain

We demonstrate that the major in vivo targets of brefeldin A (BFA) in the s ecretory pathway of budding yeast are the three members of the Sec7 domain family of ARF exchange factors: Gea1p and Gea2p (functionally interchangeab le) and Sec7p. Specific residues within the Sec7 domain are important for B FA inhibition of ARF exchange activity, since mutations in these residues o f Gea1p (sensitive to BFA) and of ARNO (resistant to BFA) reverse the sensi tivity of each to BFA in vivo and in vitro. We show that the target of BFA inhibition of ARF exchange activity is an ARF-GDP-Sec7 domain protein compl ex, and that BFA acts to stabilize this complex to a greater extent for a B FA-sensitive Sec7 domain than for a resistant one.