"Hog"ging the Promoter

Abstract

Mitogen-activated protein (MAP) kinases clearly produce many of their actions by regulating (presumably by phosphorylation) various transcription factors. But does such interaction occur in the cytoplasm or the nucleus, or in complexes formed on the promoters of target genes? Alepuz et al. show that, in the case of the Hog1 MAP kinase of Saccharomyces cerevisiae (which is required for response to osmotic stress), the last-mentioned appears to be the case. In chromatin immunoprecipitation assays (for more on this method, see Takahashi et al. ), they demonstrate association of the kinase with transcription factors in complexes at various promoters. Formation of functional complexes appeared to depend in one case on targeting of the MAP kinase to the promoter, but in others on promoter recognition by the target transcription factor Hot1. In another case, interaction of both proteins was required. Surprisingly, although Hot1 does seem to be a direct target of Hog1, this phosphorylation appeared not to be essential for transcriptional activation. In other experiments, replacement of the DNA binding domain of Hot1 with another, to target it to a new reporter gene, conferred sensitivity of that gene to osmotic stress. Thus, the authors propose that the MAP kinase could have more general effects on transcription through recruitment or regulation of the general transcription machinery. P. M. Alepuz, A. Jovanovic, V. Reiser, G. Ammerer. Stress-induced MAP kinase Hog1 is part of transcription activation complexes. Mol. Cell 7 , 767-777 (2001). [Online Journal] K. Takahashi, S. Saitoh, M. Yanagida, Application of the ChIP (chromatin immunoprecipitation) method to identify in vivo protein-DNA associations in fission yeast. Science's STKE (2001), http://stke.sciencemag.org/cgi/content/full/OC_sigtrans;2000/56/pl1 [Full Text]