LIL-Stat is constitutively activated in three leukemic cell lines. Five micrograms of nuclear protein derived from control, IL-1β(10’)-, and IL-6(10’)-treated B1 cells (lanes 1-3) and from control TF-1(lane 6) and U937 (lane 8) cells were analyzed for LIL-Stat binding activity by EMSA. Nuclear extracts were incubated with the³²P-labeled oligonucleotide LILRE, the LIL-Stat consensus sequence from the IL-1β promoter. For each cell line competition experiments were performed with a 100-fold molar excess of unlabeled LILRE oligonucleotide (lane 4, 7, and 9, respectively). Labeled LILRE oligonucleotide alone is represented in lane 5.