LBP1 (Upstream-binding protein 1), also designated UBP1, LBP1A or LBP1B, is a 540 amino acid protein that belongs to the grh/CP2 family (grainyhead transcription factor family). LBP1 is a transcriptional activator that regulates the placental expression of CYP11A1 and activates the Hemoglobin globin promoter in erythroid cells. LBP1 is responsible for repressing transcription of HIV-1 by binding to and preventing TFIID from interacting with its promoter region. Null expression of LBP1 causes uterine growth retardation in mice embryos suggesting a critical role in extraembryonic angiogenesis. LBP1 localizes to the nucleus and is expressed in adrenal tissue, Hep G2, JEG-3, and HeLa cell lines. It forms two natural variants by alternative splicing. LBP1 can form homodimers as well as heterodimers with LBP-9. LBP-9 suppresses the expression of LBP1.