AbstractBackgroundSignal transducer and activator of transcription (STAT) activation of gene expression is both rapid and transient, and when properly executed it affects growth, differentiation, homeostasis and the immune response, but when dysregulated it contributes to human disease. Transcriptional activation is regulated by alterations to the chromatin template. However, the role of histone modification at gene loci that are activated for transcription in response to STAT signaling is poorly defined.ResultsUsing chromatin immunoprecipitation, we profiled several histone modifications during STAT1 activation of the interferon regulatory factor 1 gene (IRF1). Methylated lysine histone proteins H3K4me2, H3K4me3, H3K79me3, H3K36me3 and monoubiquitinated histone ubH2B are dynamic and correlate with interferon (IFN)γ induction of STAT1 activity. Chemical inhibition of H3K4 methylation downregulatesIRF1transcription and decreases RNA polymerase II (Pol II) occupancy at theIRF1promoter. MEN1, a component of a complex proteins associated with Set1 (COMPASS)-like complex and the hBRE1 component, RNF20, are localized toIRF1in the uninduced state and are further recruited whenIRF1is activated. RNAi-mediated depletion of RNF20 lowers both ubH2B and H3K4me3, but surprisingly, upregulates IFNγ inducedIRF1transcription. The dynamics of phosphorylation in the C-terminal domain (CTD) of Pol II are disrupted during gene activation as well.ConclusionsH2B monoubiquitination promotes H3K4 methylation, but the E3 ubiquitin ligase, RNF20, is repressive of inducible transcription at theIRF1gene locus, suggesting that ubH2B can, directly or indirectly, affect Pol II CTD phosphorylation cycling to exert control on ongoing transcription.