Interaction of multiple factors with a GC-rich element within the mitogen responsive region of the human transferrin receptor gene.

Nuclear factors from HeLa cells were isolated by elution of DNA-cellulose bound proteins with a double stranded synthetic oligonucleotide corresponding to the region from -34 to -79 of the human transferrin receptor (TR) gene promoter. The eluted proteins were further purified and separated from the oligonucleotide by ion exchange chromatography. Proteins within the resulting fraction bound with specificity to the TR promoter. Retardation gel analysis and competition with specific double-stranded oligonucleotides show that multiple factors present in this fraction compete for binding within the same region of the TR promoter. Footprinting experiments demonstrate that these factors contact a GC-rich element that is within the region that is required for enhanced expression of the gene in proliferating cells. One of the factors protects an extended DNA sequence but still contacts the GC-rich element.