Enigmas of p53 tumor suppressor gene

In the review the data about the structure and functions of p53 tumor suppressor gene and its product, a nuclear phosphoprotein p53, are presented. Gene p53 is often subjected to mutations during the progression of many human tumors, becoming highly malignant. p53 protein binds sequence-specifically to DNA of eucaryotic cells and functions as a factor of transcription, suppressing the activity of many oncogenes and growth factor genes, but activating genes of some differentiation factors. Mutant p53 protein, on the contrary, is unable to bind specifically with DNA and expresses some features of oncogenes. The main function of p53 protein is the guarding of cellular genome integrity. DNA damage is catched by p53 as a signal for the induction of p21 synthesis, an inhibitor of cyclin-dependent kinases and the proliferative nuclear antigen PCNA. The double block arrests the cell on a boundary of G(1)/S phases (G(1) block). Block G(2) caused by the uncompleted DNA replication is also realized with the participation of p53. Both blocks enable a cell to enter the mitosis with repaired and completely replicated DNA. Protein p53 plays also an essential role in the programmed cell death - apoptosis.