Evidence for the Presence of a Guanine Quadruplex Forming Region within a Polypurine Tract of the Hypoxia Inducible Factor 1α Promoter<sup>†</sup>

The promoter of the hypoxia inducible factor 1 alpha (HIF-1α) gene has a polypurine/polypyrimidine tract (−65 to −85) overlapping or adjacent to several putative transcription factor binding sites, and we found that mutagenesis of this region diminished basal HIF-1α expression. Oligonucleotides representing this region of the HIF-1α promoter were analyzed by electrophoretic mobility shift, chemical probing, circular dichroism, and DNA polymerase arrest assays. The guanine-rich strand was found to form a parallel, unimolecular quadruplex in the presence of potassium that was further stabilized by two known quadruplex binding compounds, the cationic porphyrin TmPyP4 and the natural product telomestatin, while TmPyP2, a positional isomer of TmPyP4, did not stabilize quadruplex formation. These data suggest that a quadruplex structure may form in a region of the HIF-1α promoter that regulates basal HIF-1α expression.