Expression of Candida albicans Sfu1 in fission yeast complements the loss of the iron-regulatory transcription factor Fep1 and requires Tup co-repressors.

The opportunistic pathogenic yeast Candida albicans contains a gene which encodes a putative member of the iron-regulatory GATA factor protein family. This protein, referred to as suppressor of ferric uptake (Sfu1), has two Cys(2)/Cys(2)-type zinc finger domains separated by a conserved Cys-rich region. In Schizosaccharomyces pombe, the GATA-type transcription factor Fe protein 1 (Fep1) represses target gene expression when iron levels exceed those needed by the cell. To ascertain the functional similarity between Sfu1 and Fep1, the C. albicans Sfu1 was expressed in Sz. pombe cells lacking the endogenous fep1(+) gene. We determined that Sfu1 is capable of suppressing iron-related phenotypes of fep1Delta mutant cells. Using a functional SFU1-GFP fusion allele, the Sfu1 protein was localized to the nucleus under both iron-replete and iron-starved conditions. Sfu1 effectively regulated the expression of genes encoding components of the reductive and non-reductive iron transport systems. Furthermore, the iron-responsive regulation mediated by Sfu1 was GATA-dependent. The N-terminal 250 amino acid segment of Sfu1 expressed in and purified from Escherichia coli specifically associated with the hexanucleotide sequence AGATAA in an iron-dependent manner. On the other hand, expression of the full-length C. albicans Sfu1 in Sz. pombe fep1Delta tup11Delta tup12Delta triple mutant cells failed to repress target gene expression under conditions of high iron concentration. Using two-hybrid analysis, we demonstrated that Tup11 and Tup12 physically interacted with Sfu1. Taken together, these results reveal a remarkable functional conservation between Sfu1 from C. albicans and Fep1 from Sz. pombe in their ability to sense excess iron and respond by repressing target gene transcription. Copyright 2007 John Wiley & Sons, Ltd.