The Sp transcription factor family includes Sp1, Sp2, Sp3 (SPR-2) and Sp4 (SPR-1). Sp transcription factors share similar structures but do not share similar functions. All four proteins contain a highly conserved DNA-binding domain composed of three zinc fingers at the C-terminus. Sp3 binds to GT and GC boxes in promoters and can either stimulate or repress transcription. Multiple isoforms of Sp3 exist due to alternative splicing events.
