Abstract: Potassium is the major intracellular cation in most living cells, including yeasts. Although K(+) has been demonstrated to be necessary for diverse cellular functions, such as enzyme activation, additional, still uncharacterized cellular targets may exist. We show here that in Saccharomyces cerevisiae short-term potassium deprivation impacts in the mRNA level of over one thousand genes. Lack of potassium drastically alters sulfur metabolism (mainly Met and Cys metabolism), triggers an oxidative stress response and activates the retrograde pathway, possibly due to the ammonium accumulation that occurs through the Trk1 potassium transporter. We also observe a remarkable halt in the expression of genes required for ribosome biogenesis and translation, a decrease in expression of diverse components (cyclins, protein kinases) required for progression through the cell cycle and a blockage in septins assembly. Only specific subsets of these changes were observed in a strain deleted for the TRK1 and TRK2 genes growing in the presence of sufficient potassium (50?mM). Therefore, a shortage of potassium in the environment triggers an acute transcriptional response, which covers different aspects of the cell biology so far unexplored, and whose investigation will likely reveal novel functional roles for this cation.