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.