A nuclear factor that recognizes the metal-responsive elements of human metallothionein IIA gene.

Expression of metallothionein (MT) genes is regulated by heavy metals mainly at the transcriptional level, via cis-acting elements called the metal-responsive elements (MREs). A HeLa cell nuclear factor that recognizes MREs of the human MTIIA (hMTIIA) gene, MREBP, was characterized. Mobility shift assay and DNase I footprinting experiments showed that MREBP binds specifically to several MREs present upstream of the hMTIIA gene. Cadmium and zinc ions inhibited binding of MREBP to a MRE at high concentrations, suggesting a role of MREBP in the negative regulation of the hMTIIA gene. MREBP was partially purified by passing the HeLa nuclear extract over heparin-agarose, Sephacryl S-300, and MRE-Sepharose affinity columns. Blotting experiments showed that a polypeptide with an M(r) of 112,000 is responsible for the MREBP activity.