This is a hypoxia-inducible factor-1 19-mer fragment. HIF-1 functions as master regulator of response to oxygen homeostasis. Hypoxia-induced gene expression is initiated when HIF-1subunit is stabilized in response to a lack of oxygen. This part of HIF-1 binds to the von Hippel-Lindau factor (VHL) an E3 ubiquitin ligase, and the proline 564 is absolutely vital to the binding process.