Identification of multiple metal regulatory elements in mouse metallothionein-I promoter by assaying synthetic sequences.

Metallothionein genes are transcriptionally regulated by a number of inducers including heavy metals. Previous mutational analyses of the mouse metallothionein-I gene (mMTI) promoter have delineated a heavy-metal regulatory region between -60 and -42 relative to the transcription start site. A synthetic copy of a 12-base-pair (bp) conserved sequence located within this region was subsequently shown to confer heavy-metal regulation on a heterologous gene. However, specific disruption of this metal regulatory element (MRE) within a wild-type mMTI promoter reduced but did not eliminate the heavy-metal response. The additional metal regulatory activity was localized to an upstream region containing four sequences homologous to the identified MRE. Similar sequences were also found in multiple copies in metallothionein genes from other species. Here we test synthetic copies of all five mMTI MRE homologues for metal regulatory activity. At least four of these sequences are able to confer heavy-metal regulation on a heterologous promoter.