Abstract
Cells trigger massive changes in gene expression upon environmental fluctuations. The Hog1 stress-activated protein kinase (SAPK) is an important regulator of the transcriptional activation program that maximizes cell fitness when yeast cells are exposed to osmostress. Besides being associated with transcription factors bound at target promoters to stimulate transcriptional initiation, activated Hog1 behaves as a transcriptional elongation factor that is selective for stress-responsive genes. Here, we provide insights into how this signaling kinase functions in transcription elongation. Hog1 phosphorylates the Spt4 elongation factor at Thr42 and Ser43 and such phosphorylations are essential for the overall transcriptional response upon osmostress. The phosphorylation of Spt4 by Hog1 regulates RNA polymerase II processivity at stress-responsive genes, which is critical for cell survival under high osmostress conditions. Thus, the direct regulation of Spt4 upon environmental insults serves to stimulate RNA Pol II elongation efficiency.
Highlights
Cells sense and robustly respond to environmental fluctuations to maximize cell fitness
Major changes in gene expression are associated with cell exposure to environmental changes and several aspects of mRNA biogenesis appear to be targeted by Stress-Activated Protein Kinase (SAPK)
We systematically purified a subset of 40 TAP-tagged proteins involved in transcriptional elongation and subjected them to an in vitro phosphorylation assay with active Hog1 (S1 Fig)
Summary
Cells sense and robustly respond to environmental fluctuations to maximize cell fitness. The coordinated expression of such stressresponsive gene reprogramming is accomplished by the regulation of several steps in mRNA biogenesis and mRNA fate through the Hog SAPK (reviewed in [5,6]) This signaling kinase associates with chromatin [7,8] to target RNA Pol II to stress-responsive genes in order to bypass the general down-regulation of gene expression that occurs during stress conditions [4,9]. Hog associates with the coding regions of osmo-dependent genes, where it acts as a transcription elongation factor specific for stress-responsive genes [21] How this SAPK regulates elongation of stress-dependent genes still remains to be elucidated
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