Changes in environmental conditions might be a stress factor for yeast cells. There are several mechanisms of stress tolerance, developed by the cell, which activate when the stress appears. Different transcription factors coordinate the expression of stress response genes. Msn2/4p regulate the expression of the general stress response. Heat shock defense involves heat shock proteins (Hsp), controlled by Hsf1p. Osmotic shock induces the MAP kinase cascade (HOG), whereas the oxidative stress response requires the YAP network. Fungicide resistance is mediated mainly by the activity of membrane transporters and changes in the structure of the plasma membrane.