Interacts with the basal transcription machinery by coordinating the formation of a multiprotein complex at the C-FOS promoter, and linking specific signal responsive activator complexes. Promotes the formation of stable high-order complexes of SRF and PHOX1 and interacts cooperatively with PHOX1 to promote serum-inducible transcription of a reporter gene deriven by the C-FOS serum response element (SRE). Acts as a coregulator for USF1 by binding independently two promoter elements, a pyrimidine-rich initiator (Inr) and an upstream E-box (By similarity). Required for the formation of functional ARID3A DNA-binding complexes and for activation of immunoglobulin heavy-chain transcription upon B-lymphocyte activation (By similarity). Homodimer (Potential). Interacts with SRF and PHOX1. Binds a pyrimidine-rich initiator (Inr) and a recognition site (E-box) for upstream stimulatory factor 1 (USF1). Associates with the PH domain of Bruton's tyrosine kinase (BTK) (By similarity). May be a component of a BHC histone deacetylase complex that contains HDAC1, HDAC2, HMG20B/BRAF35, KDM1A, RCOR1/CoREST, PHF21A/BHC80, ZMYM2, ZNF217, ZMYM3, GSE1 and GTF2I. Interacts with BTK and ARID3A (By similarity). Interacts with isoform beta of PRKG1 (By similarity). Colocalizes with BTK in the cytoplasm. Transiently phosphorylated on tyrosine residues by BTK in response to B-cell receptor stimulation. Phosphorylation on Tyr-248 and Tyr-379, and perhaps, on Tyr-484 contributes to BTK-mediated transcriptional activation (By similarity). Sumoylated. Belongs to the TFII-I family.