Transfected pro-B cell clones conditionally overexpressing NFIL3/E4BP4. (A) Antibody-perturbed electrophoretic mobility shift assay of FL5.12 clones expressing NFIL3/E4BP4 from the zinc-regulated pMT-CB6+ expression plasmid. Solid arrowheads indicate NFIL3/E4BP4–DNA complexes from each of four independent clones grown in the presence (even lanes) or absence (odd lanes) of zinc, in the presence of IL-3 for 24 hr (+IL-3, Upper) or 16 hr after its removal (−IL-3, Lower). (B) A time course of NFIL3/E4BP4 binding activity in FL5.12 cells bearing the empty zinc-regulated vector (Upper) or the vector containing NFIL3/E4BP4 (clone 9; Lower). The mobility assay was performed with extracts from cells cultured in the presence (lanes 6–10) or absence (lanes 1–5) of zinc, and in the presence of IL-3 (lanes 1 and 6), or at the indicated intervals after its removal. Solid arrowheads indicate NFIL3/E4BP4–DNA complexes that supershifted with E4BP4 antiserum.