COPPER-SPECIFIC TRANSCRIPTIONAL REPRESSION OF YEAST GENES ENCODING CRITICAL COMPONENTS IN THE COPPER TRANSPORT PATHWAY

Copper is an essential micronutrient that is toxic in excess, To maint ain an adequate yet non-toxic concentration of copper, cells possess s everal modes of control, One involves copper uptake mediated by genes encoding proteins that play key roles in high affinity copper transpor t, These include the FRE1-encoded Cu2+/Fe3+ reductase and the CTR1 and CTR3-encoded membrane-associated copper transport proteins, Each of t hese genes is transcriptionally regulated as a function of copper avai lability: repressed when cells are grown in the presence of copper and highly activated during copper starvation. Our data demonstrate that repression of CTR3 transcription is exquisitely copper-sensitive and s pecific, Although copper represses CTR3 gene expression at picomolar m etal concentrations, cadmium and mercury down-regulate CTR3 expression only at concentrations 3 orders magnitude greater, Furthermore, coppe r-starvation rapidly and potently induces CTR3 gene expression, We dem onstrate that the CTR1, CTR3, and FRE1 genes involved in high affinity copper uptake share a common promoter element, TTTGCTC, which is nece ssary for booth copper repression and copper starvation activation of gene expression, Furthermore, the Maclp is essential for down- or up-r egulation of the copper-transport genes, In vivo footprinting studies reveal that the cis-acting element, termed CuRE (copper-response eleme nt), is occupied under copper-starvation and accessible to DNA modifyi ng agents in response to copper repression, and that this regulated oc cupancy requires a functional MAC1 gene, Therefore, yeast cells coordi nately express genes involved in high affinity copper transport throug h the action of a common signaling pathway.