Non-Classical H1-like PARP1 Binding to Chromatosome.

Poly(ADP-ribose)polymerase 1 (PARP1) is an enzyme that interacts with chromatin during DNA repair and transcription processes; the molecular mechanisms of these processes remain to be determined. Previously, we have shown that PARP1 can bind to and reorganize nucleosomes using two modes of interaction with a mono-nucleosome, which are realized through PARP1 binding to the ends of linker DNA and to the nucleosome core. Here, it is shown that the latter mode of binding induces the reorganization of nucleosome structure and is more stable under the conditions of poly(ADP-ribosyl)ation (PARylation). The initial nucleosome structure is fully recovered after the dissociation of autoPARylated PARP1. The competition between PARP1 and linker histone H1.0 for binding to a nucleosome is mediated by the PARP1-H1.0 interaction and is affected by the length of linker DNA fragments. Longer linkers stabilize H1.0-nucleosome complexes, while shorter linkers facilitate displacement of H1.0 from the chromatosome by PARP1. PARylation removes both H1.0 and PARP1 from the complexes with nucleosomes. The data suggest that the H1.0 displacement from chromatin by PARP1 that is likely modulated by the density of nucleosomes might reduce chromatin compaction and facilitate access of PARP1-dependent DNA repair and transcription factors to nucleosome and inter-nucleosomal DNA.