HIF-1 (hypoxia inducible factor 1) is known as a transcriptional key regulator of genes involved in adaption to hypoxia. HIF-1 consists of two subunits, HIF-1a and HIF-1b. Specific proline residues (Pro564 and Pro402) of HIF-1a are oxygen dependent modified by three distinct HIF-1a prolyl hydroxylases (PHD-1, PHD-2, and PHD-3) and thus targeted for polyubiquitination leading to proteasomal degradation. These PHDs act as cellular oxygen sensors. It has been shown previously that PHD-1 is exclusively present in the nucleus, PHD2 is mainly located in the cytoplasm and PHD3 is homogeneously distributed in the cytoplasm and the nucleus. To date less is known about the mechanism of nuclear translocation of PHD-1 and PHD-3.

Here we report on the determination and characterisation of nuclear localisation signals of PHD-1 and PHD-3. Our in silico analysis of PHD-1 predicted a specific NLS for PHD-1 which was verified by mutant analysis and protein-protein interaction. For both, PHD-1 and PHD-3, the direct binding to specific proteins (importin a and b) of the classical nuclear import pathway was shown.