Multilayered control of gene expression by stress‐activated protein kinases

Stress‐activated protein kinases (SAPKs) are key elements for intracellular signalling networks that serve to respond and adapt to extracellular changes. Exposure of yeast to high osmolarity results in the activation of p38‐related SAPK, Hog1, which is essential for reprogramming the gene expression capacity of the cell by regulation of several steps of the transcription process. At initiation, active Hog1 not only directly phosphorylates several transcription factors to alter their activities, but also associates at stress‐responsive promoters through such transcription factors. Once at the promoters, Hog1 serves as a platform to recruit general transcription factors, chromatin‐modifying activities and RNA Pol II. In addition, the SAPK pathway has a role in elongation. At the stress‐responsive ORFs, Hog1 recruits the RSC chromatin‐remodelling complex to modify nucleosome organization. Several SAPKs from yeast to mammals have maintained some of the regulatory abilities of Hog1. Thus, elucidating the control of gene expression by the Hog1 SAPK should help to understand how eukaryotic cells implement a massive and rapid change on their transcriptional capacity in response to adverse conditions.