Hydroxylates HIF-1 alpha at 'Asp-803' in the C-terminaltransactivation domain (CAD). Functions as an oxygen sensor and,under normoxic conditions, the hydroxylation prevents interactionof HIF-1 with transcriptional coactivators includingCbp/p300-interacting transactivator. Involved in transcriptionalrepression through interaction with HIF1A, VHL and histonedeacetylases. Hydroxylates specific Asn residues within ankyrinrepeat domains (ARD) of NFKB1, NFKBIA, NOTCH1, ASB4, PPP1R12A andseveral other ARD-containing proteins. Also hydroxylates Asp andHis residues within ARDs of ANK1 and TNKS2, respectively.Negatively regulates NOTCH1 activity, accelerating myogenicdifferentiation. Positively regulates ASB4 activity, promotingvascular differentiation.