Hypoxia-inducible factor 3 alpha is the alpha-3 subunit of one of several alpha/beta-subunit heterodimeric transcription factors that regulate many adaptive responses to low oxygen tension (hypoxia). The alpha-3 subunit lacks the transactivation domain found in factors containing either the alpha-1 or alpha-2 subunits.

It is thought that factors containing the alpha-3 subunit are negative regulators of hypoxia-inducible gene expression. At least three transcript variants encoding three different isoforms have been found for this gene.Expressed in kidney. Expressed abundantly in lung epithelial cells. Expression is regulated in an oxygen- dependent manner.