Transcription factors Sp1 and Sp3 regulate basal transcription of the human IRF-3 gene

► A Sp1/NRF-1 binding site was involved in the IRF-3 minimal promoter activation. ► Sp1 and Sp3, but not NRF-1, positively regulate IRF-3 transcription activity. ► Sp1 and Sp3 increased expression of the IRF-3 gene at the level of transcription.