Metallothionein (MT) is a low molecular weight, cysteine-rich metal-binding protein. MTs usually contain 61 or 62 amino acids, 20 of which are cysteine residues whose thiolate sulfur atoms serve as metal ligands. MTs can bind many kinds of heavy metals such as copper, zinc, cadmium, mercury, nickel, cobalt, silver, gold, and lead. Structural analysis of MT reveals two domains including a - and b -domain. The two classes of metal ions, monovalent and divalent, appear to interact differentially with the two structural domains of MT. Monovalent ions, such as Cu+ and Ag+, are known to bind preferentially to b -domain. In contrast, divalent ions, such as Cd2+ and Zn2+, prefer to bind to a -domain. We have constructed the fusion gene between chicken MT-II and a Chlamydomonas plasma membrane protein to both anchor the MT-II domain on the exterior surface of the cell and to perhaps stabilize the protein so as to obtain higher levels of expression. Furthermore, to increase the specificity of the transgenic Chlamydomonas to monovalent or divalent ions, we have constructed fusion genes between the b - or a -domain of chicken MT-II and a Chlamydomonas plasma membrane protein. Finally, to increase the heavy metal binding capacity of the transformant, we have constructed the series of polymers of chicken MT-II, the MT-II a -domain, or the MT-II b -domain including (monomer, dimer, trimer, tetramer, and pentamer) fused to Chlamydomonas plasma membrane protein.