Abstract
The yeast MAP kinase Hog1 pathway activates transcription of several hundreds genes. Large-scale gene expression and DNA binding assays suggest that most Hog1-induced genes are regulated by the transcriptional activators Msn2/4, Hot1 and Sko1. These studies also revealed the target genes of each activator and the putative binding sites on their promoters. In a previous study we identified a group of genes, which we considered the bona fide targets of Hog1, because they were induced in response to expression of intrinsically active mutant of Hog1, in the absence of any stress. We previously analyzed the promoter of the most highly induced gene, STL1, and noticed that some promoter properties were different from those proposed by large-scale data. We therefore continue to study promoters individually and present here analyses of promoters of more Hog1's targets, RTC3, HSP12, DAK1 and ALD3. We report that RTC3 and HSP12 promoters are robust and are induced, to different degrees, even in cells lacking all four activators. DAK1 and ALD3 promoters are not robust and fully depend on a single activator, DAK1 on Sko1 and ALD3 on Msn2/4. Most of these observations could not be inferred from the large-scale data. Msn2/4 are involved in regulating all four promoters. It was assumed, therefore, that the promoters are spontaneously active in ras2Δ cells, in which Msn2/4 are known to be de-repressed. Intriguingly, the promoters were not active in BY4741ras2Δ cells, but were de-repressed, as expected, in ras2Δ cells of other genetic backgrounds. This study describes two phenomena. One, some Hog1's target promoters are most robust, backupped by many activators. Second, in contrast to most laboratory strains, the widely used BY4741 strain does not induce Msn2/4 activity when the Ras/cAMP cascade is downregulated.
Highlights
Regulation of transcription initiation is mediated primarily by transcriptional activators and suppressors that commonly function through specific cis-elements in the enhancers of their target genes [1,2,3,4]
To pick promoters for individual analysis we used the list of the bona fide target genes of Hog1 (Table 2A in ref. [21])
A strongly induced gene (~90-fold) in this list is STL1 and its promoter has already been thoroughly studied [21]. Another gene that was very strongly induced (~75-fold) in response to Hog1D170A+F318L expression is RTC3/YHR087w, which encodes a protein with currently unknown function
Summary
Regulation of transcription initiation is mediated primarily by transcriptional activators and suppressors that commonly function through specific cis-elements in the enhancers of their target genes [1,2,3,4]. To confirm directly that transcription of RTC3 could be induced by activation of Hog1 alone we introduced a RTC3-LacZ reporter to hog1Δ cells together with either an empty vector or plasmids that inducibly express either Hog1WT or Hog1D170A+F318L. Shown is β-galactosidase activity in hog1Δ cells, harboring the RTC3-LacZ reporter gene and the indicated HOG1 plasmids, under the indicated conditions.
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