(D) Structural comparison between the p53 DBD-nucleosome complex and the nucleosome containing the same DNA sequence. The atomic model of the p53 DBD-nucleosome complex is fitted into the transparent cryo-EM map. (C) Cryo-EM structure of the p53 DBD-nucleosome complex. The p53BS DNA region, which directly contacts the histone surface in the absence of p53, is highlighted. (B) Schematic illustration of the nucleosomal DNA construct containing the p53 binding sequence (193 bp 601 DNA). The transcription activation domain 1/2 (TAD1/2), proline-rich region (PRR), core DNA-binding domain (DBD), tetramerization domain (TD), and C-terminus domain (CTD) are indicated. (A) Schematic representations of the full-length p53 (p53 FL) and p53 DBD. P53 binding induces nucleosomal linker DNA release from the histone octamer. These findings suggest that defects in the sequence-specific DNA binding of p53 may be a major cause of tumorigenesis. Mutations in p53 have been found in about 50% of cancer patients, and most of the mutations are accumulated within the DBD ( 3, 4). The DBD region plays an important role in DNA binding by p53, especially for its specific interaction with the target DNA sequence, termed the p53 binding sequence (p53BS). The human p53 protein is composed of 393 amino acid residues, which form the transcription activation domain 1 (TAD1, residues 1 to 40), the transcription activation domain 2 (TAD2, residues 41 to 60), the proline-rich region (PRR, residues 61 to 93), the DNA-binding domain (DBD, residues 102 to 293), the tetramerization domain (TD, residues 323 to 353), and the C-terminal domain (CTD, residues 364 to 393) (Fig. The p53 protein is the product of a tumor suppressor gene, and functions as a transcription factor that induces the expression of genes related to cell cycle, apoptosis, senescence, and DNA repair ( 1). These results provide novel insights for understanding the mechanism by which p53, as a pioneer transcription factor, recognizes its binding sequence in chromatin. Biochemical analyses revealed that the flexible p53 C-terminal domain, which contains an additional DNA-binding domain, binds around the center and linker DNAs of the nucleosome. In the structures, p53 peels the nucleosomal DNA region containing the p53 binding DNA sequence from the histone core, and specifically binds the DNA as a tetramer. Here, we present cryo-EM structures of the p53-nucleosome complexes. In response to DNA damage, the transcription factor p53 stimulates the expression of various genes involving tumor suppressors by binding to the p53 binding DNA sequence, which is frequently embedded within the nucleosome. These results provide important structural information for understanding the mechanism by which p53 binds the nucleosome and changes the chromatin structure for gene activation. The C-terminal domain of p53 also binds to the DNA around the center and linker DNA regions of the nucleosome, as revealed by hydroxyl radical footprinting. The p53 binding peels the DNA from the histone surface, and drastically changes the DNA path around the p53BS on the nucleosome. The nucleosomal position of the p53BS DNA is within the genomic p21 promoter region. In the p53-nucleosome structures, the p53 DNA-binding domain forms a tetramer and specifically binds to the p53BS DNA, located near the entry/exit region of the nucleosome. Here we report the cryo-electron microscopy structures of the p53 DNA-binding domain and the full-length p53 protein complexed with a nucleosome containing the 20 base-pair target DNA sequence of p53 (p53BS). However, the mechanism by which p53 binds to its target DNA in the nucleosome remains elusive. The tumor suppressor p53 functions as a pioneer transcription factor that binds a nucleosomal target DNA sequence.
0 Comments
Leave a Reply. |