ROLE OF THE CONSERVED HISTIDINES IN THE ZN MODULE OF THE COPPER-ACTIVATED TRANSCRIPTION FACTORS IN YEAST

The Amt1 and Ace1 transcription factors from Candida glabrata and Sacc haromyces cerevisiae are activated by the formation of a tetracopper t hiolate cluster resulting in Cu(4)Zn(1)Amt1 complexes. An independent Zn module exists within the N-terminal 40 residues of Amt1 and Ace1. T here are two conserved histidyl residues within this module. His25 ser ves as a Zn(II) ligand for the S3N1 site. Thus, Zn(II) ligands are pro vided by cysteinyl thiolates of Cys11, Cys14, Cys23 and His25. The Zn module is a stably folded domain that binds group IIb metal ions with high affinity. Mutations in Amt1 and Ace1 genes within codons encoding Zn(II) cysteinyl ligands markedly attenuate the ability of Amt1 and A ce1 to mediate Cu-induced expression of metallothionein genes. Thus, t he Zn modules in Amt1 and Ace1 are functionally important. A second hi stidine, His18, is conserved in the Zn module of these metal-activated factors. His18 does not serve a major structural role, but appears im portant functionally in Ace1 and Amt1.