Zinc dependent binding of a liver nuclear factor to metal response element MRE-a of the mouse metallothionein-l gene and variant sequences

Abstract

Metallothionein gene transcription is inducible by zinc and other heavy metals, and several metal response elements (MREs) have been mapped within about 200 bp upstream of the site of transcription initiation in several metallothionein genes. Comparison of a number of MREs defined a 15 bp consensus sequence containing a more highly conserved MRE core sequence TGCRCNCG. I have used the proximal MRE of the mouse metallothionein-I gene (MRE-a) in DNA fragment mobility shift assays to detect a protein in rat liver nuclear extracts which binds specifically to the MRE in a zinc-regulated manner. Use of a comprehensive series of variant MRE sequences established that the binding was strongly dependent on the MRE core sequence, whereas changes at the less highly conserved positions had minor effects on binding. This provides strong evidence that the protein detected is responsible for the zinc-responsiveness of the MT genes in liver, and provides a more detailed picture of the regulatory protein:MRE interaction than was previously available.