Recent studies have demonstrated that p53 binds to specific DNA sequences and the consensus sequence for the p53 binding site has been proposed. The p53 binding site has also been shown to act as positive p53-responsive element. Here we report the identification of a GC3 element that enhances p53-mediated transactivation when placed adjacent to the consensus p53 site. The GC3 element alone cannot act as a positive p53-responsive element. We also show that p53 activates transcription of the c-erbA-alpha gene through a DNA element that consists of the p53 quarter-sites and GC3 elements. Using gel mobility-shift assay, we identified a possible GC3 binding factor distinct from p53.