Identification of a single-stranded DNA-binding protein that interacts with an S1 nuclease-sensitive region in the platelet-derived growth factor A-chain gene promoter

We previously observed that transcription of the platelet-derived growth factor (PDGF) A-chain gene is enhanced in cells stimulated by PDGF through a serum response element (SRE) in its 5'-flanking sequence. We now show that the region of the SRE is sensitive to S1 nuclease in vitro. We also identify a single-stranded DNA-binding protein in HeLa cell nuclear extracts that binds to the noncoding strand of the PDGF A-chain SRE but not to its double-stranded counterpart or to the single-stranded coding sequence. Competition assays using oligonucleotides with sequence-specific mutations that diminished or eliminated detectable complex formation were used to establish the specificity of this protein/DNA interaction. Remarkably, the sequence-specific single-stranded binding protein binds to this region only when it is highly supercoiled. The data suggest that the single-stranded DNA-binding protein specifically interacts with a highly supercoiled region of the PDGF A-chain promoter and that this interaction may have a role in the transcriptional regulation of this gene.