Native Cadmium-Metallothionein from the Yeast Saccharomyces cerevisiae: Its Primary Structure and Function in Heavy-Metal Resistance

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A Cd-resistant strain of yeast (Saccharomyces cerevisiae, strain 301N) accumulated Cd with the concomitant synthesis of a Cd-binding protein of low molecular weight when grown in Cd^<2+>-containing medium. Analysis of the amino acid composition, N-terminal sequence and immunological properties of the protein revealed its structural homology to Cu-metallothionein (Cu-MT) in S. cerevisiae 2186, a Cu-resistant strain of yeast (Winge et al. 1985). The synthesis of MT in Cu-resistant strains of yeast is known to be under the strict control of Cu^<2+> ions, while that in 301N was induced both by Cd^<2+> and Cu^<2+> ions. When 301N was precultured for 48 h in the presence of 1 mM CuSO_4, its resistance to Cu^<2+> and the synthesis of MT in response to Cu^<2+> were enhanced while analogous responses to Cd^<2+> were conversely reduced. These results suggest that the synthesis of MT is controlled by Cd^<2+> and Cu^<2+> in a counteractive manner in strain 301N and, therefore, the regulation of the synthesis of MT plays a role in the adaptation of this strain to conditions when either metal is present.
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