Abstract
Regulated expression of the Ena1 Na+-ATPase is a crucial event for adaptation to high salt and/or alkaline pH stress in the budding yeast Saccharomyces cerevisiae. ENA1 expression is under the control of diverse signaling pathways, including that mediated by the calcium-regulatable protein phosphatase calcineurin and its downstream transcription factor Crz1. We present here a quantitative study of the expression of Ena1 in response to alkalinization of the environment and we analyze the contribution of Crz1 to this response. Experimental data and mathematical models substantiate the existence of two stress-responsive Crz1-binding sites in the ENA1 promoter and estimate that the contribution of Crz1 to the early response of the ENA1 promoter is about 60%. The models suggest the existence of a second input with similar kinetics, which would be likely mediated by high pH-induced activation of the Snf1 kinase.
Highlights
Excessive intracellular concentration of sodium cations is deleterious for most eukaryotic cells and, diverse mechanisms to avoid cytosolic accumulation of this cation have been evolutionarily developed
The yeast Saccharomyces cerevisiae, often used as a model to study the mechanisms of cation homeostasis, resorts to both sequestration of sodium into organelles and to extrusion of this cation through transporters located at the cell membrane [1]
The promoter activity of ENA1 was calculated from the data recently obtained from our Genomic Run On (GRO) analysis [27] of the changes caused by sudden transition from pH 5.5 to a moderate alkalinization
Summary
Excessive intracellular concentration of sodium cations is deleterious for most eukaryotic cells and, diverse mechanisms to avoid cytosolic accumulation of this cation have been evolutionarily developed. The yeast Saccharomyces cerevisiae, often used as a model to study the mechanisms of cation homeostasis, resorts to both sequestration of sodium into organelles (mainly the vacuole) and to extrusion of this cation through transporters located at the cell membrane [1]
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