Regulation of Genome-Wide Transcriptional Stress Responses in Saccharomyces cerevisiae

Abstract

In response to osmotic shock in Saccharomyces cerevisiae the MAP kinase Hog1 coordinates a large-scale transcriptional stress response, rapidly producing hundreds of copies of specified transcripts. Many of the most highly induced genes are bound and regulated by a transcription factor, Sko1, but lack the canonical binding site for this factor. We use ChIP-seq to demonstrate a stress-specific binding mode of Sko1. In stress, Sko1 binds to promoters in close proximity to Hog1, and another Hog1-regulated transcription factor, Hot1. This mode of Sko1 binding requires the physical presence of Hog1, but not Hog1 phosphorylation of Sko1. We identify candidate Sko1 and Hot1 binding motifs that predict co-localization of Sko1, Hot1, and Hog1 at promoters. We then demonstrate a role for Sko1 and Hot1 in directing Hog1-associated RNA Pol II to target genes, where Hog1 is present with the elongating polymerase. We suggest a possible model for Hog1 reprogramming of transcription in the early stages of the osmotic stress response. We then determine the extent and structure of the Hog1 controlled transcriptional program in a related stress, damage to the cell wall. We find that Sko1 and Hot1 have different apparent thresholds for activation by Hog1. In addition, in cell wall damage, Hog1 regulates an additional transcription factor, Rlm1, that is not involved in other Hog1 regulated stress responses. This factor is activated by the coincidence of a signal from Hog1 with that of another MAP kinase, Slt2.