MOLECULAR-CLONING AND EXPRESSION OF A METALLOTHIONEIN MESSENGER-RNA IN XENOPUS-LAEVIS

Metallothioneins (MT) are expressed during early development in specie s of several groups. To understand MT function in developmental proces ses, we studied the MT system of Xenopus laevis, a model vertebrate sp ecies in experimental embryology. We first purified and sequenced the liver MT from copper-treated animals. This 62-amino-acid protein share s the main structural properties of known vertebrate MT, and is more c losely related to avian than to fish or mammalian MT. Using this seque nce, we designed oligonucleotide primers to amplify and isolate a MT c lone from a XL2 cell line cDNA library. This 752-bp cDNA encodes a put ative 62-amino-acid-long protein that is 100% identical with the seque nced MT. Zinc, cadmium, and copper ions are very efficient inducers of MT mRNA accumulation in Xenopus liver and cell lines.