The von Hippel-Lindau tumor suppressor protein (pVHL) has been shown to bind directly to the alpha subunits of the heterodimeric transcription factor HIF (hypoxia inducible factor). pVHL directs the polyubiquitination and, hence, destruction of HIF in the presence of oxygen. Loss of pVHL function leads to deregulation of HIF target genes, which play critical roles in angiogenesis.