Steroids regulate alternative splicing of RUSH/SMARCA3. The full-length, progesterone-dependent isoform and the 3'-truncated, estrogen-dependent isoform have identical DBDs, NLSs and RING fingers. Transcription of RUSH/SMARCA3 is mediated by a bipartite progesterone receptor half-site/overlapping Y-box combination (-38/-26), where progesterone activation is attenuated by NF-Y binding. Regulation also involves two GC-rich sequences in the proximal promoter (-162/+90) and a RUSH/SMARCA3 site (-616/-611) in the 5'-UTR. Isoform specific-binding to the RUSH/SMARCA3 site is dictated by the hormonal milieu, as is the availability of factors that bind to the distal GC-rich site (-131/-126), a composite binding site for Egr-1/Sp1/3/MAZ/MZF1/c-Rel, and the proximal GC-rich site (-62/-53), which binds only Sp1/3. TransSignal TF-TF Interaction arrays, supershift assays, and ChIP analyses confirmed strong physical interactions between RUSH/Egr-1 and RUSH/c-Rel that were visualized with fluorescent microscopy. Higher-order, long-range interactions between RUSH and Egr-1/c-Rel derivative of the anisotropic flexibility of the intervening DNA sequence were shown by 3C assay. GST-pull-downs confirmed the RING finger is the protein-binding domain suggesting the RUSH isoforms have equivalent potential for protein interactions. Transient transfection assays showed the cooperative interaction between RUSH and Egr-1 mediates repression by c-Rel. Thus progesterone-induced transcription is fine-tuned by isoform-specific autoregulation, in which newly synthesized RUSH-1 binds DNA, interacts physically with liganded Egr-1 in the proximal promoter via a DNA-looping mechanism, to mediate repression by c-Rel. In the absence of progesterone induction, RUSH-1 replaces RUSH-1 binding, Egr-1 and c-Rel are unavailable as molecular ties, and DNA looping is disfavored.