Iron must cross biological membranes to reach essential intracellular
enzymes. Two proteins in the plasma membrane of yeast-a multicopper ox
idase, encoded by the FET3 gene, and a permease, encoded by the FTR1 g
ene-were shown to mediate high-affinity iron uptake. FET3 expression w
as required for FTR1 protein to be transported to the plasma membrane.
FTR1 expression was required for apo-FET3 protein to be loaded with c
opper and thus acquire oxidase activity. FTR1 protein also played a di
rect role in iron transport. Mutations in a conserved sequence motif o
f FTR1 specifically blocked iron transport.