Atrans-acting factor necessary for optimal CD23 transcription is limiting in pt1-LCL^tetcells. (A) Schematic diagram of the pGL23a and pGL23b constructs denoting the approximate positions of the specific promoters and downstream genes encoded in the plasmid. LCL^tet cells (pt1: ▪; D11: □; and C2: ▦), cultured continuously in the presence of tet, were transiently cotransfected with pGL23a/b constructs and either the pRL-SV40 (B) or the pRL-TK (C) control plasmids. Luciferase activity was assayed 48 hours after transfection. Results are shown as relative light units with SEM of at least 3 independent experiments with P < .1 (*) or P < .05 (**).