Hypoxia-inducible factor 1(HIF₁) is a nuclear factor whose production and DNA binding activity is induced by hypoxia in a variety of cell types, which is composed of two different subunits: 120 ku HIF_1α and 91～94 ku HIF_1β. HIF₁, as a hypoxia inducible transcription factor, promotes the expression of erythropoietin gene and glycolytic enzymes gene etc. in response to hypoxia which maintain the oxygen homeostasis.