cDNA cloning and cadmium-induced expression of metallothionein mRNA in thezebra mussel Dreissena polymorpha

Using pooled degenerate oligonucleotides inferred from the N-terminal amino acid sequence of Dreissena polymorpha metallothionein and a Cys-X-Cys moti f characteristic for known metallothioneins, a 150-bp metallothionein-speci fic reverse transcription PCR product was generated. The PCR product was us ed to screen a Dreissena polymorpha cDNA library, and a complete metallothi onein cDNA sequence from Dreissena was identified. Four clones with the ide ntical sequence were detected, Supporting the idea of a single metallothion ein gene in Dreissena. The sequence contains a 141-bp 5' untranslated regio n-and a 572-bp 3' untranslated region with two polyadenylation signals. The coding region spans 219 bp. The deduced amino acid sequence shows 21 cyste ine residues present in the metallothionein-typical motifs. Induction studi es were performed with 50 mu g Cd2+/L for up to 16 days. The exposed mussel s show a sevenfold higher metallothionein mRNA level compared with uninduce d control mussels.