H3K4me3 regulates RNA polymerase II promoter-proximal pause-release

Trimethylation of histone H3 lysine 4 (H3K4me3) is associated with transcriptional start sites and proposed to regulate transcription initiation. However, redundant functions of the H3K4 SET1/COMPASS methyltransferase complexes complicate elucidation of the specific role of H3K4me3 in transcriptional regulation. Here, by using mouse embryonic stem cells (mESCs) as a model system, we show that acute ablation of shared subunits of the SET1/COMPASS complexes leads to complete loss of all H3K4 methylation. H3K4me3 turnover occurs more rapidly than H3K4me1 and H3K4me2 and is dependent on KDM5 demethylases. Surprisingly, acute loss of H3K4me3 does not have detectable effects on transcriptional initiation but leads to a widespread decrease in transcriptional output, an increase in RNA polymerase II (RNAPII) pausing and slower elongation. Notably, we show that H3K4me3 is required for the recruitment of the Integrator Complex Subunit 11 (INTS11), which is essential for the eviction of paused RNAPII and transcriptional elongation. Thus, our study demonstrates a distinct role for H3K4me3 in transcriptional pause-release and elongation rather than transcriptional initiation.