The p53 transcriptional pathway. A simplified scheme is shown for genes regulated by p53. In some cases, such as for GADD45 (28), CIP1/W1P1 (17), and MDM2 (5,38), p53 binding sites have been identified in regulatory regions of these genes; the inclusion of others, such as PIG] to PIG14 (43), is based on induction by p53 expression vectors.