Anti-Sp1 transcription factor antibodies are used in the immunodetection of the protein encoded by the SP1 gene. In humans, the canonical protein has a reported length of 785 amino acid residues and a mass of 80.7 kDa. Its subcellular localization is in the nucleus and cytoplasm. Alternative splicing is reported to yield 3 different isoforms for this protein. A member of the Sp1 C2H2-type zinc-finger protein family, it is reported to be a transcription factor that can activate or repress transcription in response to physiological and pathological stimuli. Post-translational modifications have been described, including O-glycosylation, ubiquitination, sumoylation, acetylation, protein cleavage and phosphorylation. Other names for this target antigen include transcription factor Sp1 and specificity protein 1.