(A) Cooperative transactivation of the neutrophil elastase promoter by c-myb and either p32 or p30 isoforms of C/EBPɛ. Expression plasmids (500 ng) or empty vectors were cotransfected with 4 μg of either the NELuc reporter or reporter plasmids mutated at either the C/EBP or myb site. Combination of C/EBPɛ and c-myb were 1.5-fold to twofold more active than the additive effect of both factors alone. Binding of both factors to their DNA motif was required for cooperation. (▪) Wild-type; (▨) C/EBP site mutant; () Myb site mutant. (B) Effect of spacing between C/EBP and c-myb binding sites in neutrophil elastase promoter on transcritional activation by C/EBPɛ p30 and c-myb. Two constructs with the insertion of either 5 (NELuc +5) or 10 bp (NELuc +10) between the binding sites were used. (C) Cooperative transactivation of mim-1 promoter (−240 to +150) Luc reporter plasmid with c-myb and either the p32 or p30 isoforms of C/EBPɛ or C/EBP. Expression plasmids or empty vectors (500 ng) were cotransfected with reporter plasmid (4 μg) into CV-1 cells. Luciferase activity was assayed after 40 hours.