A HUMAN METAL-RESPONSIVE ELEMENT-BINDING PROTEIN INTERACTS WITH A HOMOLOGOUS ELEMENT OF THE MOUSE METALLOTHIONEIN-I GENE

Metallothionein (MT) is thought to play a central role in the detoxification of heavy metals, and thus studies on its regulation are toxicologically important. Heavy metal-dependent induction of MT genes is mediated by metal responsive elements (MREs) located upstream of the genes. Zinc regulatory factor (ZRF) is a zinc-dependent MRE-binding protein that was originally detected in HeLa cell nuclear extracts using the most proximal MRE of the human MT-IIA gene (hMREa) as a probe. We show that ZRF in HeLa cell nuclear extracts can also bind to the most potent MRE of the mouse MT I gene (mMREd). This finding was further confirmed by using partially purified ZRF. Moreover, cadmium could not promote complex formation between ZRF and mMREd at any concentration tested, as is also the case with ZRF and hMREa. These observations suggest that the transcriptional regulatory system of MT genes by zinc is conserved beyond species.