Metal regulatory elements of the mouse metallothionein-I gene.

The promoter of the mouse metallothionein-I (mMT-I) gene contains multiple metal regulatory elements (MREs) which allow transcription of the gene to be induced by heavy metals. Insertion into the promoter of the TK gene of two or more synthetic MREs enables that gene to respond to heavy metals. We tested each of the MREs from the mMT-I promoter in this assay, and found four to be functional. We have commenced a systematic analysis of single nucleotide changes within an MRE, to determine the contribution of each nucleotide. The MRE core sequence in which single nucleotide changes can abolish function is TGCRCNCG; certain changes outside this sequence have lesser effects. MREs can act cooperatively with distal promoter elements of the TK gene, but in the presence of just a TATA-box they function as heavy-metal dependent promoter elements. Experiments to determine the effect of spacing suggest a range of at least 90 bp for interaction of two MREs, but the range for efficient stimulation of transcription from a TATA-box appears to be shorter. Stimulation of MT gene transcription by heavy metals is probably mediated by heavy metal-activated regulatory proteins binding cooperatively to the multiple MREs.