Dissection of Rag1 promoter activity using extrachromosomal reporter assays. (A) Diagram shows conserved binding sites for transcription factors within the Rag1 promoter, with numbering relative to the transcription start site. (B and C) Activity of wild-type and mutant Rag1 promoters tested in luciferase reporters containing a wild-type or mutated 1.2-kb ASE downstream of the luciferase gene. Plasmids were assayed for luciferase activity following transient transfection into VL3-3M2 cells. The data represent mean ± SEM of four independent experiments, with values normalized to those for wild-type Rag1p + ASE in each experiment and the average value for Rag1p + ASE set as 1. **, P < 0.01 ***, P < 0.001; ****, P < 0.0001 by one-way ANOVA with Holm-Sidak’s multiple comparisons test.