Effect of heme and vacuole deficiency on FRE1 gene expression and ferrireductase activity in Saccharomyces cerevisiae

We have examined the effects of heme or vacuole deficiency on the kinetics of induction of cell surface ferrireductase activity and expression of the FRE1 gene encoding a component of ferrireductase, in response to iron or copper deprivation in S. cerevisiae. Heme deficiency caused a small decrease in the basal expression of FRE1, but did not impair its induction by Fe or Cu limitation. Thus, the absence of ferrireductase activity and its non-inducibility in heme-less cells is not due to the absence of FRE1 expression. Vacuole deficiency led to constitutively high ferrireductase activity slightly induced by Cu limitation, and to high levels of FRE1 expression further inducible by Fe or Cu deprivation. Thus, the vacuole might be a component of the iron signalling pathway.