Fig. 5. Two-state model of RNAP2-Ser5ph– and H3K27ac-enriched chromatin domains.

Inside the nucleus, two distinct sites are characterized by enrichment for RNAP2-Ser5ph or H3K27ac with little overlap. H3K27ac-enriched regions represent poised chromatin, which is slightly denser than average chromatin but has increased single nucleosome mobility. In combination, these factors reinforce 3D target searching, increasing the probability of contact between genetic elements or interacting proteins. RNAP2-Ser5ph–enriched regions are areas of high transcriptional activity, where chromatin is decondensed but stabilized by the presence of bound transcription machinery.