Defining TP53 pioneering capabilities with competitive nucleosome binding assays

Area of Science:

• Molecular Biology
• Genetics
• Epigenetics

Background:

• Accurate gene expression relies on transcription factors (TFs) accessing DNA within nucleosomes.
• Pioneer factors are a special class of TFs that can bind to TF binding sites (TFBS) within nucleosomes.
• TP53 is suggested to be a pioneer factor, but its nucleosome binding mechanism is unclear.

Purpose of the Study:

• To comprehensively examine how TP53 binds to nucleosomal DNA.
• To determine the influence of TFBS location, affinity, and nucleosome position on TP53 binding.
• To validate in vitro findings in a cellular context.

Main Methods:

• In vitro binding assays with purified TP53 and reconstituted nucleosomes.
• Competitive binding experiments with varying TFBS affinities and positions.
• Next-generation sequencing to quantify TP53-nucleosome complex formation.
• Validation in a cell line model to observe TP53-induced binding.

Main Results:

• TP53 preferentially binds to nucleosome edges, with binding inhibited near the dyad.
• Nucleosome position is a primary determinant of TP53 binding, overriding TFBS affinity.
• TP53 exhibits strong nonspecific nucleosome binding, aiding chromatin interaction.
• In cells, TP53 binding is induced at nucleosome edges adjacent to nucleosome-free regions.

Conclusions:

• TP53's pioneer factor activity is driven by nonspecific binding to nucleosome edges.
• Specific binding occurs at nucleosome edges, facilitating access to regulatory DNA.
• Understanding TP53-nucleosome interactions is crucial for gene expression regulation.