Hypoxia-inducible factors (HIFs) are heterodimeric transcription factors that regulate adaptive responses to low oxygen tension.
HIFs are composed of alpha subunits, such as HIF3A, and beta subunits, both of which belong to the superfamily of proteins containing basic helix-loop-helix (bHLH), PER as PER1 (MIM.602260), ARNT (MIM.126110), SIM as SIM1 (MIM.603128) (PAS) domains.