The inhibition of the iron responsive element RNA-protein interaction by heme does not mimic in vivo iron regulation

Hemin at > 1 μM concentrations inhibits the interaction of the iron responsive element (IRE) and the iron responsive element binding protein (IRE-BP) as measured by gel retardation and UV cross-linking. Heme has recently been proposed to inhibit the repression of translation of an IRE-containing mRNA (Lin, J.J., Daniels-McQueen, S., Patino, M.M., Gaffield, L., Walden, W.E., and Thach, R.E. (1990) Science 247, 74-76). Our binding inhibition provides structural support for these observations. The action of heme, however, does not mimic the physiologically demonstrated inhibition of high affinity binding of the IRE to IRE-BP by the oxidation of a sulfhydryl of the IRE-BP. In addition to this effect, hemin also inhibits a wide variety of RNA and DNA binding proteins, restriction endonucleases, and nucleases. Therefore, in vitro, the inhibitory effects of hemin are not limited to the interaction of the IRE-BP and the IRE, but are nonspecific and affect a wide variety of nucleic acid-protein interactions. Any hypothesis on the effects on protein-nucleic acid interactions employing > 1 μM concentrations of hemin should be interpreted with caution.