Hydroxylates HIF-1 alpha at 'Asn-799' in the C-terminal transactivation domain (CAD). Functions as an oxygen sensor and, under normoxic conditions, the hydroxylation prevents interaction of HIF-1 with transcriptional coactivators including Cbp/p300-interacting transactivator. Involved in transcriptional repression through interaction with HIF1A, VHL and histone deacetylases. Hydroxylates specific Asn residues within ankyrin repeat domains (ARD) of NFKB1, NFKBIA, NOTCH1, ASB4, PPP1R12A and several other ARD-containing proteins. Also hydroxylates Asp and His residues within ARDs of ANK1 and TNKS2, respectively. Negatively regulates NOTCH1 activity, accelerating myogenic differentiation (By similarity). Positively regulates ASB4 activity, promoting vascular differentiation. 2-oxoglutarate + L-asparaginyl-[hypoxia-inducible factor alpha subunit] + O2 = (3S)-3-hydroxy-L-asparaginyl-[hypoxia-inducible factor alpha subunit] + CO2 + succinate 2-oxoglutarate + L-histidyl-[ankyrin-repeat domain protein] + O2 = (3S)-3-hydroxy-L-histidyl-[ankyrin-repeat domain protein] + CO2 + succinate 2-oxoglutarate + L-asparaginyl-[ankyrin-repeat domain protein] + O2 = (3S)-3-hydroxy-L-asparaginyl-[ankyrin-repeat domain protein] + CO2 + succinate 2-oxoglutarate + L-aspartyl-[ankyrin-repeat domain protein] + O2 = (3S)-3-hydroxy-L-aspartyl-[ankyrin-repeat domain protein] + CO2 + succinate Homodimer; homodimerization is essential for catalytic activity. Interacts with VHL and HIF1A. Part of a complex with VHL, HIF1A and HDAC1 or HDAC2 or HDAC3. Interacts with NFKB1 and NFKBIA. Interacts with NOTCH1, NOTCH2 and NOTCH3 but not with NOTCH4. Interacts with ABPA3. Interacts with TNKS2. Interacts with PPP1R12A (By similarity). Interacts with UBE3A (By similarity). Interacts with ASB4. Interacts with ANKS3 (PubMed:25671767). Interacts with NECAB3; the interaction is indirect and seems to be mediated by APBA3 (By similarity).