The gene for cadmium metallothionein from a cadmium-resistant yeast appears to be identical to CUP1 in a copper-resistant strain.

A cadmium-resistant strain of Saccharomyces cerevisiae produces a cadmium metallothionein with the same characteristics as the copper metallothionein that is encoded by CUP1 in a copper-resistant strain. The structural gene for metallothionein from the cadmium-resistant strain resembles CUP1 in terms of the fragmentation patterns generated by restriction enzymes. Furthermore, the gene may be amplified as 2.0 kb repeating units in both the cadmium-resistant and the copper-resistant strains. However, transformants with a plasmid that carried the metallothionein gene from the cadmium-resistant strain were resistant to copper but not to cadmium. It appears that the same metallothionein gene, CUP1, is amplified in both cadmium- and copper-resistant yeasts. However, the mechanism for the cadmium-specific inducibility of the gene may be restricted to the cadmium-resistant strain.