ZAP1P, A METALLOREGULATORY PROTEIN INVOLVED IN ZINC-RESPONSIVE TRANSCRIPTIONAL REGULATION IN SACCHAROMYCES-CEREVISIAE

Zinc ion homeostasis in Saccharomyces cerevisiae is controlled primari ly through the transcriptional regulation of zinc uptake systems in re sponse to intracellular zinc levels, A high-affinity uptake system is encoded by the ZRT1 gene, and its expression is induced more than 30-f old in zinc-limited cells, A low-affinity transporter is encoded by th e ZRT2 gene, and this system is also regulated by zinc. We used a gene tic approach to isolate mutants whose ZRT2 expression is no longer rep ressed in zinc-replete cells, and a new gene, ZAP1, was identified, ZA P1 encodes a 93-kDa protein with sequence similarity to transcriptiona l activators; the C-terminal 174 amino acids contains five C2H2 zinc f inger domains, and the N terminus (residues 1 to 706) has two potentia l acidic activation domains. The N-terminal region also contains 12% h istidine and cysteine residues, The mutant allele isolated, ZAP1-I-up, is semidominant and caused high-level expression ZRT1 and ZRT2 in bot h zinc-limited and zinc-replete cells, This phenotype is the result of a mutation that substitutes a serine for a cysteine residue in the N- terminal region, A zap1 deletion mutant grew well on zinc-replete medi a but poorly on zinc-limiting media, This mutant had low-level ZRT1 an d ZRT2 expression in zinc-limited as well as zinc-replete cells. These data indicate that Zap1p plays a central role in zinc ion homeostasis by regulating transcription of the zinc uptake system genes in respon se to zinc, Finally, we present evidence that Zap1p regulates transcri ption of its arm promoter in response to zinc through a positive autor egulatory mechanism.