The work presented here intends to address the question of whether the immediate/early promoter of cytomegalovirus (CMV), which is widely used for expressing transgenes in eukaryotic cells, yields a constitutive expression of the transgenes under stress conditions in Saccharomyces cerevisiae cells. This information would also be relevant because in the tetracycline-regulated expression (tetO) system, which is one of the first choices for studying gene function from yeast to human cells, the CMV promoter controls the expression of the tetO transactivator. We found that the CMV promoter in yeast cells is bidirectionally induced by osmotic stress and in glycerol media. The mitogen-activated protein (MAP) kinase Hog1 controls CMV activation by osmotic stress through the ATF/CRE-related transcription factor Sko1 and the yeast osmostress factor Hot1. Our results indicate that the CMV and tetO expression systems respond to external signals and this should be considered before using these systems in yeast. Moreover, our results also suggest that CMV could be regulated by the intracellular glucose concentration in human cells.