Histone acetyltransferase 2 links H4 acetylation, H2A.Z deposition and transcription start site-choice in African trypanosomes

Both, acetylation of histones and of histone variant H2A.Z are conserved features of eukaryotic transcription start sites (TSSs) and both features appear to be critical for correct transcription initiation. However, complex patterns of transcriptional regulation have complicated the establishment of functional links between histone acetylation, H2A.Z deposition and their importance in transcription regulation. To elucidate these links, we took advantage of the unusual genome organization in Trypanosoma brucei, a highly divergent eukaryote. In T. brucei genes are organized in long polycistronic transcription units, drastically reducing the sites of transcription initiation. Employing a highly sensitive and quantitative mass-spectrometry-based approach, we quantified the genome-wide histone acetylation and methylation pattern and identified various acetyl and methyl marks exclusively enriched at TSSs In addition, we show that deletion of histone acetyltransferase 2 results in a loss of H4 acetylation at TSSs, a loss of H2A.Z deposition at TSSs and a shift in the sites of transcription initiation. Combined, our findings demonstrate an evolutionary conserved link between histone H4 acetylation, H2A.Z deposition and RNA transcription initiation.