THE IDENTIFICATION, CLONING AND CHARACTERIZATION OF EARTHWORM METALLOTHIONEIN

Combining standard gel chromatographic techniques and novel molecular methodologies (Directed Differential Display and quantitative PCR), it has been possible to isolate and sequence two isoforms of the first t rue earthworm metallothionein. Both proteins are characteristically hi gh in cysteine residues and possess no significant aromatic residues. Metal responsiveness was confirmed by determining metallothionein spec ific expression profiles in earthworms exposed to soils of differing h eavy metal concentrations, Analysis of the derived amino acid sequence of isoform 2 identified two putative N-glycosylation signal sequences , suggesting that the two isoforms may have different subcellular dist ributions and functions. Possible implications for intracellular metal trafficking are discussed. (C) 1998 Federation of European Biochemica l Societies.