Anti-regulatory factor X4 antibodies are used in the immunodetection of the protein encoded by the RFX4 gene. In humans, the canonical protein has a reported length of 735 amino acid residues and a mass of 83.4 kDa. Its subcellular localization is in the nucleus. Alternative splicing is reported to yield 4 different isoforms for this protein. A member of the RFX protein family, it is reported to be a transcription factor that plays a role in early brain development. Other names for this target antigen include transcription factor RFX4, regulatory factor X, 4 (influences HLA class II expression), testis development protein NYD-SP10, winged-helix transcription factor RFX4, and NYD-SP10.