The p53 protein is an unusually shaped tetramer that binds directly to DNA

We have analyzed the size and structure of native immunopurified human p53 protein. By using a combination of chemical crosslinking, gel filtration chromatography, and zonal velocity gradient centrifugation, we have determined that the predominant form of p53 in such preparations is a tetramer. The behavior of purified p53 in gels and sucrose gradients implies that the protein has an extended shape. Wild-type p53 has been shown to bind specifically to sites in cellular and viral DNA. We show in this study by Southwestern ligand blotting and by analysis of DNA-bound crosslinked p53 that p53 monomers, dimers, and tetramers can bind directly to DNA.