Siderophore-iron uptake in Saccharomyces cerevisiae -: Identification of ferrichrome and fusarinine transporters

A family of four putative transporters (Arn1p-4p) in Saccharomyces cerevisiae is expressed under conditions of iron deprivation and is regulated by Aft1p, the major iron-dependent transcription factor in yeast. One of these, Arn3p/Sit1p, facilitates the uptake of ferrioxamine B, a siderophore of the hydroxamate class. Here we report that ARN family members facilitated the uptake of iron from the trihydroxamate siderophores ferrichrome, ferrichrome A, and triacetylfusarinine C. Uptake of siderophore-bound iron was dependent on either the high-affinity ferrous iron transport system or the ARN family of transporters. The specificity of each siderophore for individual transporters was determined. Uptake of ferrichrome and ferrichrome A was facilitated by both Arn1p and Arn3p. Uptake of triacetylfusarinine C was facilitated by Arn2p, although small amounts of uptake also occurred through Arn1p and Arn3p. In contrast to the trihydroxamates, uptake of iron from the dihydroxamate rhodotorulic acid occurred only via the high-affinity ferrous iron system. Epitope-tagged Arn1p was expressed in intracellular vesicles in a pattern that was indistinguishable from that of Arn3p, whereas Ftr1p, a component of the high-affinity ferrous system, was expressed on the plasma membrane. These data indicate that S. cerevisiae maintains two systems of siderophore uptake, only one of which is located on the plasma membrane.