Osmotic Stress-Induced Gene Expression in Saccharomyces cerevisiae Requires Msn1p and the Novel Nuclear Factor Hot1p

Abstract

After a sudden shift to high osmolarity, Saccharomyces cerevisiae cells respond by transiently inducing the expression of stress-protective genes. Msn2p and Msn4p have been described as two transcription factors that determine the extent of this response. In msn2 msn4 mutants, however, many promoters still show a distinct rise in transcriptional activity upon osmotic stress. Here we describe two structurally related nuclear factors, Msn1p and a newly identified protein, Hot1p (for high-osmolarity-induced transcription), which are also involved in osmotic stress-induced transcription.hot1 single mutants are specifically compromised in the transient induction of GPD1 and GPP2, which encode enzymes involved in glycerol biosynthesis, and exhibit delayed glycerol accumulation after stress exposure. Similar to a gpd1 mutation, a hot1 defect can rescue cells from inappropriately high HOG pathway activity. In contrast, Hot1p has little influence on the osmotic stress induction of CTT1, where Msn1p appears to play a more prominent role. Cells lacking Msn1p, Msn2p, Msn4p, and Hot1p are almost devoid of the short-term transcriptional response of the genes GPD1,GPP2, CTT1, and HSP12 to osmotic stress. Such cells also show a distinct reduction in the nuclear residence of the mitogen-activated protein kinase Hog1p upon osmotic stress. Thus, Hot1p and Msn1p may define an additional tier of transcriptional regulators that control responses to high-osmolarity stress.

ACKNOWLEDGMENTS

The first three authors have contributed equally to this publication.

We are grateful to C. Schüller (Vienna, Austria) for helpful discussions and critically reading the manuscript, to A. Marchler-Bauer (Vienna, Austria) for first pointing out to us the similarity between HOT1 and MSN1 sequences, and to H. Saito (Boston, Mass.) and H.-J. Schüller (Greifswald, Germany) for providing plasmids.

We acknowledge support from the Commission of the European Union via contracts BIO4-CT95-0161 to J.M.T. and S.H. and FMRX-CT96-0007 to J.M.T., H.R., and S.H. The Vienna groups have also been supported by grants P10815 and P12478 (to H.R.) and W001 (predoctoral fellowship to V.R.) from the Fonds zur Förderung der wissenschaftlichen Forschung, Vienna, Austria.