Reciprocal binding of PARP-1 and histone H1 at promoters specifies transcriptional outcomes.

Nucleosome-binding proteins act to modulate the promoter chromatin architecture and transcription of target genes. We used genomic and gene-specific approaches to show that two such factors, histone H1 and poly(ADP-ribose) polymerase-1 (PARP-1), exhibit a reciprocal pattern of chromatin binding at many RNA polymerase II-transcribed promoters. PARP-1 was enriched and H1 was depleted at these promoters. This pattern of binding was associated with actively transcribed genes. Furthermore, we showed that PARP-1 acts to exclude H1 from a subset of PARP-1-stimulated promoters, suggesting a functional interplay between PARP-1 and H1 at the level of nucleosome binding. Thus, although H1 and PARP-1 have similar nucleosome-binding properties and effects on chromatin structure in vitro, they have distinct roles in determining gene expression outcomes in vivo.