MAC1, a nuclear regulatory protein related to Cu-dependent transcription factors is involved in Cu/Fe utilization and stress resistance in yeast

The related transcription factors ACE1 of Saccharomyces cerevisiae and AMT1 of Candida glabrata are involved in copper metabolism by activating the transcription of copper metallothionein genes. ACE1 and AMT1 are 'copper-fist' transcription factors which possess a conserved cysteine-rich copper binding domain required for DNA binding. Here we report the identification of a nuclear protein from S.cerevisiae, MAC1, whose N-terminal region is highly similar to the copper and DNA binding domains of ACE1 and AMT1. Loss-of-function mutants of MAC1 have a defect in the plasma membrane Cu(II) and Fe(III) reductase activity, are slow growing, respiratory deficient, and hypersensitive to heat and exposure to cadmium, zinc, lead and H₂O₂. Conversely, a dominant gain-of-function mutant of MAC1 shows an elevated reductase activity and is hypersensitive to copper. We have identified two target genes of MAC1 whose altered expression in mutants of MAC1 can account for some of the observed mutant phenotypes. First, MAC1 is involved in basal level transcription of FRE1, encoding a plasma membrane component associated with both Cu(II) and Fe(III) reduction. Second, MAC1 is involved in the H₂O₂-induced transcription of CTT1, encoding the cytosolic catalase. This suggests that MAC1 may encode a novel metal-fist transcription factor required for both basal and regulated transcription of genes involved in Cu/Fe utilization and the stress response.