Molecular biology and environmental induction of piscine metallothionein

To investigate the factors involved in the control of metallothionein (MT) expression in fish, genomic clones encoding the MTs from the Cd-tolerant fish (pike and stone loach) were isolated. Sequencing revealed putative metal regulatory elements (MREs) in the 5′-regions of both MT genes. Comparison of their composition and location showed little distinction between different fish species. However, although high overall homology exists between fish MTs and their mammalian counterparts, the 5′-regions of the fish genes are distinct, not only in the organisation of their MREs but also in the absence of other transcription factor binding sites.