PARP1-Dependent Alterations in Nucleosome Organization: Potential Involvement of p53

Chromatin of eukaryotic organisms is a complexly organized and dynamic complex. Chromatin proteins provide proper regulation of gene expression, DNA replication, and DNA repair. Among the most important regulators of chromatin architecture among nonhistone proteins are p53 and poly(ADP-ribose) polymerase 1 (PARP1), which are involved in the cellular response to DNA damage. In the present study, the authors investigated the cooperative and competitive binding of the DNA-binding domain (DBD) of p53 and the enzyme PARP1 to mononucleosomes reconstituted on the Widom 603 sequence with an embedded p53 binding site. To detect interactions, the electrophoretic mobility shift assay method with fluorescently labeled DNA was used. Complexes were formed in two ways: nucleosomes were preincubated with p53DBD and then PARP1 was added, or the nucleosome–PARP1 complex was formed first and then p53DBD was introduced. The results showed that the order of protein addition determines the nature of their interaction with the nucleosome: at low p53DBD concentrations, displacement of this protein by PARP1 is observed, while stable nucleosome–p53DBD complexes undisturbed by PARP1 are formed at higher p53DBD concentrations. No stable ternary nucleosome–p53DBD–PARP1 complexes were detected.