Three proteins involved in hypoxia response, molecular model. The three proteins involved in the hypoxia response are the aryl hydrocarbon receptor nuclear translocator (ARNT, yellow ribbon), endothelial PAS domain-containing protein (EPAS, blue ribbon) and coiled-coil co-activator (CCC, pink ribbon). When combined, the three proteins form the hypoxia-inducible factor complex (HIF), a DNA (deoxyribonucleic acid) transcription factor which plays a role in physiological responses to hypoxia (lack of oxygen).