How p53 binds DNA as a tetramer

The p53 tumor suppressor protein is a tetramer that binds sequence‐specifically to a DNA consensus sequence consisting of two consecutive half‐sites, with each half‐site being formed by two head‐to‐head quarter‐sites (→← →←). Each p53 subunit binds to one quarter‐site, resulting in all four DNA quarter‐sites being occupied by one p53 tetramer. The tetramerization domain forms a symmetric dimer of dimers, and two contrasting models have the two DNA‐binding domains of each dimer bound to either consecutive or alternating quarter‐sites. We show here that the two monomers within a dimer bind to a half‐site (two consecutive quarter‐sites), but not to separated (alternating) quarter‐sites. Tetramers bind similarly, with the two dimers within each tetramer binding to pairs of half‐sites. Although one dimer within the tetramer is sufficient for binding to one half‐site in DNA, concurrent interaction of the second dimer with a second half‐site in DNA drastically enhances binding affinity (at least 50‐fold). This cooperative dimer–dimer interaction occurs independently of tetramerization and is a primary mechanism responsible for the stabilization of p53 DNA binding. Based on these findings, we present a model of p53 binding to the consensus sequence, with the tetramer binding DNA as a pair of clamps.

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