Three Dβ1 promoter probes bind the similar set of nuclear proteins. (A) Diagram of TCR Dβ1 promoter. GC-rich and GATA motifs in the Dβ1 promoter and major transcription start sites (from Doty et al²⁴ ) are shown. (B) EMSA using nuclear extracts from the p5424 cell line were performed using labeled probes representing the 3 GC-rich motifs with no competitor or with competitors representing sequences with wild-type or mutant GC-rich motifs for the -35 probe (p35 or p35m), the -281 probe (p281 or p281m), or the -314 probe (p314 or p314m).