COPPER-MEDIATED REPRESSION OF THE ACTIVATION DOMAIN IN THE YEAST MAC1P TRANSCRIPTION FACTOR

The expression of a number of genes encoding products involved in copp er ion uptake in yeast is specifically inhibited by copper ions. We sh ow here that copper metalloregulation occurs through Cu-dependent repr ession of the transactivation activity of Mac1p. A segment of the yeas t transcription factor Mac1p was identified that activated transcripti on in vivo in a heterologous system using fusion polypeptides with the yeast Gal4 DNA-binding domain. The Gal4/Mac1p hybrid exhibits transac tivation activity that is repressed in cells cultured in the presence of copper salts and derepressed in cells with reduced copper uptake. T he repressive effect is specific for copper ions. The concentration de pendency of the Cu-inactivation of Gal4/Mac1p is similar to that of Cu -inhibition of CTR1 expression, a known Cu-regulated gene in vivo. Cop per inhibition of gene expression is not observed with a Gal4/Mac1p ch imera containing the MAC1(up1) substitution within the transactivation domain. Cells harboring the MAC1(up1) allele fail to attenuate FRE1 a nd CTR1 expression in a Cu dependent manner. Additional MAC1(up) allel es exist within the first of two cysteine-rich sequence motifs adjacen t to the His --> Gin MAC1(up1) encoded substitution. Thus, Cu-regulati on of Mac1p function arises from a novel Cu-specific repression of the transactivation domain function. Models for the mechanism of Cu-repre ssion of Mac1p function will be discussed.