Characterisation of six additional human metallothionein genes.

Human metallothionein (MT) genes are clustered in a locus on chromosome 16, and this report presents the characterisation of the remaining six univestigated members of the family. Nucleotide sequencing in whole or part suggested that four of these genes, MT1I, MT1J, MT1K and MT1L do not encode expressed MT proteins, based on the presence of structural faults or atypical amino acid assignments. On the other hand, the structures of MT1H and MT1X are consistent with these genes being functional and encoding unique type 1 isoforms. The promoters of both genes conferred activity to CAT expression constructs when transfected into HeLa cells, and showed differential responses to inducers MT synthesis. Endogenous MT1H and MT1X genes were expressed at the mRNA level in HeLa cells following cadmium treatment. This work brings the number of functional class 1 and 2 MT genes in the human to eight, and confirms that each encodes structurally unique proteins.