Induction of C/EBP binding activities by IL-7. BM B220⁺/IgM⁻ pre-B cells were isolated by FACS sorting as detailed in Materials and Methods. BM pre-B lymphocytes and 70Z/3 pre-B cells were stimulated with IL-7 (10 ng/mL) for 2 hours or left untreated. Nuclear extracts were prepared and incubated with [³²P]-labeled C/EBP double-strand oligonucleotide, as described in Materials and Methods. Unlabeled competitor probe was used at 100-fold molar excess. One milliliter of the indicated anti-C/EBP antisera or of preimmune rabbit serum was added to the reaction mixtures. The results of a single experiment are shown as a representative of four other independent experiments.