Hydroxylates a specific Asn residue in the C-terminal transactivation domain (CAD) of HIF-1 alpha. The hydroxylation prevents interaction of HIF-1 with transcriptional coactivators. Also hydroxylates specific Asn, Asp and His residues within ankyrin repeat domain-containing proteins. 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.