IRE binding activity of IRP1 and IRP2 in LY cells. (A) Cell extracts were prepared as previously described.19 20 Four micrograms of protein were analyzed for IRE binding by IRP1 in the presence or absence of 2% 2-ME. (B) Radioactivity associated with IRE-IRP1 complexes without (open bars) or with (solid bars) 2% 2-ME was quantified with phosphorimaging, and signals are plotted in arbitrary units. (C) Ten micrograms of protein were analyzed for IRE binding by IRP2 in the presence or absence of 0.5% 2-ME. Because signals given by IRP2-IRE complexes are weaker than those of IRP1-IRE complexes, they were amplified and shown separately. Experiments are representative of 5 that gave similar results.