Carol Prives Department of Biological Sciences Columbia University New York, New York 10027

~ 53 plays a critical role in transducing a signal from damaged DNA to genes that control the cell cycle and apoptosis. Intrinsic to its function in this pathway is the ability of~ 53, a tetrameric phosphoprotein, to bind sequence specifically to DNA. This property allows~ 53 to serve as a transcriptional activator. Several~ 53 target genes have been identified that contain a~ 53 response element that conforms to the consensus sequence (5-RRRC AIT TIA G YY Y-33*. Tumor-derived~ 53 mutants almost invariably display abnormal DNA binding and transcriptional activation properties. These and other relevant facts have been discussed in recent reviews (Levine, 1993; Prives and Manfredi, 1993). p53 Mutations in Cancer Experimental manipulation of the~ 53 gene and protein has been useful for unveiling its functions and domains. However, there has been an equally powerful and revealing set of information about~ 53 that has not been derived by experimentation-that resulting from sequencing the tumor-derived~ 53 genes of nearly 2000 cancer patients (Figure 1; Lin et al., 1994; Hollstein et al., 1994). When aligned with the sequence of~ 53 and compared with what is now known about its functions and properties, these mutants provide an extraordinary view of the~ 53 protein. First, thevast majority of the mutationsare clustered within the central portion of the protein, where 4 of the 5 regions that are highly conserved among all~ 53 genes sequenced to date are located. Second, although mutation of the great majority (but not all) of the amino acids within the center of p53 has occurred in tumors, there are among these a number of “hot spots” that occur with unusually high frequency. This spectrum of~ 53 mutations tells us that central to the role of~ 53 in preventing cancer is the very center of p53 itself.

The Domains of p53 Reverse genetic and biochemical approaches have been used to assign domains, functions, and sites within~ 53. Domains of~ 53 defined in terms of separable activities that contribute to its overall function include a transcrip tional activation region at the N-terminus (residues l-43)(Unger et al., 1992, and references therein); a sequencespecific DNA-binding domain (residues 100-300)(Bargonetti et al., 1993; Halazonetis and Kandil, 1993; Pavletich et al., 1993; Wang et al., 1993); an oligomerization domain that dictates that the protein form stable tetramers (residues 320-360)(Sturzbecher et al., 1992; Pavletich et al., 1993; Wang et al., 1993); and a nonspecific nucleic acidbinding (and reannealing) region (residues 330-393)(Wang et al., 1993, and references therein). Experiments with proteases have also been informative (Figure 1).~ 53 has two protease-resistant domains: one within the central portion, extending roughly between