Identification of novel histone marks required for the transcriptional stress response

Upon environmental stresses such as temperature fluctuations or increases in osmolarity, yeast Saccharomyces cerevisiae induces a transcriptional reprograming in order to survive and adapt to the stress. Histone post-translational modifications are key regulatory elements known to modulate transcription. By using a complete collection of histone mutants, we performed a high throughput transcriptional screening to assess the histone residues required for a proper induction of stress-responsive fluorescent reporters upon heat and osmotic stress. From our screening, we could extract general conclusions regarding the histone residues required for the stress-induced transcription. We observed poor overlap between the residues necessary for heat and osmotic stress. Results from the screening also suggested accessible and modifiable residues were more prone to affect stress-induced transcription when mutated. Following such indications, we selected the accessible and modifiable residues H4-S47 and H4-T30 as their mutation rendered transcriptional defects upon osmotic and heat stress respectively. We validated and characterized the extent of their transcriptional defects by northern blot and RNA sequencing. We also identified and characterized Cla4 and Ste20 for H4-S47 and Ste11 for the H4-T30 as the putative kinases phosphorylating these residues upon stress. In addition, the study of other residues identified in the screening opens new possibilities to identify novel histone modifications relevant for the transcriptional stress response.