Which histone modification activates transcription?
Active promoter epigenetic signature includes specific histone methylation. H3 lysine 4 trimethylation deposited by SET1 and MLL complexes at transcription start sites recruits chromatin remodelers, histone acetyltransferases and general transcription factor TFIID via TAF3 PHD finger recognition, reducing nucleosome stability and stimulating preinitiation complex assembly and pause release. Conversely H3K9 trimethylation and H3K27 trimethylation deposited by SUV39H and Polycomb EZH2 cause repression. H4K20 trimethylation marks pericentric heterochromatin. Thus H3K4 trimethylation functions as universal epigenetic hallmark of actively transcribed euchromatic genes across eukaryotes.
Ref: Santos-Rosa et al., Nature 2002; Alberts et al., Molecular Biology of the Cell, Chapter 4: H3K4me3 Active Transcription