USE OF GENETIC SUPPRESSOR ELEMENTS TO DISSECT DISTINCT BIOLOGICAL EFFECTS OF SEPARATE P53 DOMAINS

p53 is a multifunctional tumor suppressor protein involved in the nega tive control of cell growth. Mutations in p53 cause alterations in cel lular phenotype, including immortalization, neoplastic transformation, and resistance to DNA-damaging drugs. To help dissect distinct functi ons of p53, a set of genetic suppressor elements (GSEs) capable of ind ucing different p53-related phenotypes in rodent embryo fibroblasts wa s isolated from a retroviral library of random rat p53 cDNA fragments. All the GSEs were 100-300 nucleotides long and were in the sense orie ntation. They fell into four classes, corresponding to the transactiva tor (class I), DNA-binding (class II), and C-terminal (class III) doma ins of the protein and the 3'-untranslated region of the mRNA (class I V). GSEs in all four classes promoted immortalization of primary cells , but only members of classes I and III cooperated with activated ras to transform cells, and only members of class III conferred resistance to etoposide and strongly inhibited transcriptional transactivation b y p53. These observations suggest that processes related to control of senescence, response to DNA damage, and transformation involve differ ent functions of the p53 protein and furthermore indicate a regulatory role for the 3'-untranslated region of p53 mRNA.