ENHANCED EFFECTIVENESS OF COPPER-ION BUFFERING BY CUP1 METALLOTHIONEIN COMPARED WITH CRS5 METALLOTHIONEIN IN SACCHAROMYCES-CEREVISIAE

The bakers' yeast Saccharomyces cerevisiae contains a metallothionein (MT) gene family comprised of the amplified CUP1 locus and the single copy CRS5 gene, We demonstrate that CUP1 plays the dominant role in co pper detoxification, A single copy of CUP1 was far more effective in c onferring copper resistance than was CRS5. The CUP1 promoter contribut es to this resistance; in a promoter exchange experiment, the Crs5 MT conferred strong copper resistance when its expression was driven by t he CUP1 promoter, and conversely, the CRS5 promoter reduced the effect iveness of Cup1 MT, Unlike CUP1, the CRS5 promoter appears to be refra ctory to high concentrations of copper, The CUP1 coding sequences also contribute to copper tolerance, presumably reflecting the enhanced bi nding avidity of Cup1 MT for Cu(I) ions, In studies with the bathocupr oine Cu(I) chelator, the Cu(I) ions bound to Crs5 were kinetically mor e labile than the Cu(I) binding to Cup1. Our findings are consistent w ith the assembly of Crs5 into two metal-binding clusters, similar to m ammalian MTs, but unlike Cup1. Overall, the striking differences in ge ne structure regulation, and function of CUP1 and CRS5 are remarkably reminiscent of the MTI and MTII genes of the pathogenic yeast Candida glabrata.