Immunoaffinity chromatography of a cellular tumor antigen from mouse neuroblastoma cells

The cellular tumor antigen p53 was isolated from mouse neuroblastoma cells and was found in a form not complexed to another protein. The p53 in these cells was stable, turning over about every 10 h. Its methionine-labelled tryptic peptides were very similar to those of the p53 isolated from SV40-transformed mouse cells. The labelled protein was purified from neuroblastoma cells by immunoaffinity using specific monoclonal antibodies and was about 80% radiochemically pure. Furthermore, the purified p53 sedimented in sucrose gradients with a sedimentation coefficient of approximately 8S. This correlated with the sedimentation coefficient of p53 prior to purification, showing that the purified protein retained its native size.