Endothelial PAS domain-containing protein 1 is a transcription factor involved in the induction of genes regulated by oxygen, which is induced as oxygen levels fall. The encoded protein contains a basic-helix-loop-helix domain protein dimerization domain as well as a domain found in proteins in signal transduction pathways which respond to oxygen levels.a bHLH-PAS transcription factor that induces EPO (133170) gene expression in cultured cells in response to hypoxia. Like HIF1A, EPAS1 binds to and activates transcription from the HIF1A response element derived from the 3-prime flanking region of the EPO gene. Activation by both HIF1A and EPAS1 is stimulated by hypoxic conditions. EPAS1 heterodimerizes with ARNT (126110) and requires ARNT for transcriptional activation of target genes.