P53 DOMAINS - STRUCTURE, OLIGOMERIZATION, AND TRANSFORMATION

Wild-type p53 forms tetramers and multiples of tetramers. Friedman et al. (P. N. Friedman, X. B. Chen, J. Bargonetti, and C. Prives, Proc. N atl. Acad. Sci. USA 90:3319-3323, 1993) have reported that human p53 b ehaves as a larger molecule during gel filtration than it does during sucrose gradient sedimentation. These differences argue that wild-type p53 has a nonglobular shape. To identify structural and oligomerizati on domains in p53, we have investigated the physical properties of pur ified segments of p53. The central, specific DNA-binding domain within murine amino acids 80 to 320 and human amino acids 83 to 323 behaves predominantly as monomers during analysis by sedimentation, gel filtra tion, and gel electrophoresis. This consistent behavior argues that th e central region of p53 is globular in shape. Under appropriate condit ions, however, this segment can form transient oligomers without appar ent preference for a single oligomeric structure. This region does not enhance transformation by other oncogenes. The biological implication s of transient oligomerization by this central segment, therefore, rem ain to be demonstrated. Like wild-type p53, the C terminus, consisting of murine amino acids 280 to 390 and human amino acids 283 to 393, be haves anomalously during gel filtration and apparently has a nonglobul ar shape. Within this region, murine amino acids 315 to 350 and human amino acids 323 to 355 are sufficient for assembly of stable tetramers . The finding that murine amino acids 315 to 360 enhance transformatio n by other oncogenes strongly supports the role of p53 tetramerization in oncogenesis. Amino acids 330 to 390 of murine p53 and amino acids 340 to 393 of human p53, which have been implicated by Sturzbecher et al. in tetramerization (H.-W. Sturzbecher, R. Brain, C. Addison, K. Ru dge, M. Remm, M. Grimaldi, E. Keenan, and J. R. Jenkins, Oncogene 7:15 13-1523, 1992), do not form stable tetramers under our conditions. Our findings indicate that p53 has at least two autonomous oligomerizatio n domains: a strong tetramerization domain in its C-terminal region an d a weaker oligomerization domain in the central DNA binding region of p53. Together, these domains account for the formation of tetramers a nd multiples of tetramers by wild-type p53. The tetramerization domain is the major determinant of the dominant negative phenotype leading t o transformation by mutant p53s.