An electrophoretic mobility shift assay demonstrating HIF-1 in nuclear extracts from src wild-type and src-deficient cells. An electrophoretic mobility shift assay demonstrating the presence of binding activity induced by hypoxia (HIF-1) to radiolabeled oligonucleotide E24, which contains the HIF-1–binding site from the murine erythropoietin 3′ enhancer. Nuclear extracts were prepared from embryonic mouse fibroblasts lacking src (src⁻) or wild-type cells possessing src (src wt) exposed to normoxia (21% oxygen) or hypoxia (1% oxygen) for 1 (1h) and 2 hours (2h). The inducible species and the constitutive species are indicated. The time course and binding of the inducible species does not differ between wild-type and src⁻ cells.