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.