Cloning and characterization of a gene coding for a novel metallothionein in the Pacific oyster Crassostrea gigas (CgMT2): a case of adaptive response to metal-induced stress?

Cases of heavy metal resistance acquisition have already been demonstrated in eukaryotes, which involve metallothionein (MT) gene duplication or ampli fication mechanisms. We characterized in a marine bivalve, Crassostrea giga s, a gene coding for an unusual MT, Which has never been described in other species. Our results illustrate a unique case of exon duplication and rear rangement in the MT gene family. The particular organization of the third e xon of this gene allows the synthesis of a NIT that presents a higher metal ion binding capacity compared to previously described MTs. The formation o f a supplementary third structural beta -domain is proposed to explain resu lts obtained in in vitro experiments. Differences in the metal responsive e lement (MRE) copy number and MRE core sequence observed in the promoter of CgMT2 also suggest differential regulation of CgMT2 transcription and possi ble implication in the detoxification processes. (C) 2001 Elsevier Science B.V. All rights reserved.