HIF1A and neoplasm: Next we examined HIF-1α protein levels in the isolated tumors by western blotting and could observe reduced levels of HIF-1α protein in ∆Np73−/− tumors compared to wild-type (Fig. 2a, b), which remained significant after normalizing to tumor size (Supplementary Fig. 3C), suggesting that the reduction in HIF-1α protein levels is due to loss of ∆Np73 and not due to differences in tumor size.