p53 is a well-known tumor suppressor that is mutated in over 50% of human cancers. These mutations were shown to exhibit gain of oncogenic function compared with the deletion of the gene. Additionally, p53 has fundamental roles in differentiation and development; nevertheless, mutant p53 mice are viable and develop malignant tumors only on adulthood. We set out to reveal the mechanisms by which embryos are protected from mutant p53-induced transformation using ES cells (ESCs) that express a conformational mutant of p53. We found that, despite harboring mutant p53, the ESCs remain pluripotent and benign and have relatively normal karyotype compared with ESCs knocked out for p53. Additionally, using high-content RNA sequencing, we show that p53 is transcriptionally active in response to DNA damage in mutant ESCs and elevates p53 target genes, such as p21 and btg2. We also show that the conformation of mutant p53 protein in ESCs is stabilized to a WT conformation. Through MS-based interactome analyses, we identified a network of proteins, including the CCT complex, USP7, Aurora kinase, Nedd4, and Trim24, that bind mutant p53 and may shift its conformation to a WT form. We propose this conformational shift as a novel mechanism of maintenance of genomic integrity, despite p53 mutation. Harnessing the ability of these protein interactors to transform the oncogenic mutant p53 to the tumor suppressor WT form can be the basis for future development of p53-targeted cancer therapy.T he tumor protein 53 (p53) transcription factor (encoded by the human gene TP53/TRP53) is a key tumor suppressor and a master regulator of genomic stability, cell cycle, DNA repair, senescence, and apoptosis (1). p53 function is frequently compromised during tumorigenesis, usually as a result of somatic mutations, which occur in more than 50% of human cancers (2). These mutants were shown to exhibit gain of oncogenic functions in addition to the loss of WT activity, leading to an aggressive malignant phenotype (2). Most TP53 mutations can be classified into two main categories: DNA contact and conformational mutations. The first group is composed of mutations in residues that directly bind the DNA, the second group of mutations causes distortion of the core domain folding and inhibits p53 from binding the DNA and transactivating its target genes. These mutations affect p53 conformation in a dynamic fashion, which at least partially depends on its binding partners in a cell context-dependent manner (3).Over the years, researchers have developed several mouse models as tools for investigating p53, including p53 KO mice (4) and mice knocked in for mutant p53 (Mut) (5, 6). These models showed the role of p53 as a regulator of developmental and differentiation processes. For instance, p53 KO mice were found to display developmental abnormalities, such as upper incisor fusion, ocular abnormalities, polydactyly of the hind limbs, and exencephaly (7). On the cellular level, ES cells (ESCs) were found to express high levels of p53 mRNA and protein, which...