Saccharomyces Cerevisiae

The ability to sense and respond to changes in environmental nutrient levels is critical for life. Yeast cells, such as Saccharomyces cerevisiae, have the ability to sense and adapt to nutrient levels in their external and internal environment. This ability to sense and adapt to nutrient levels play an essential role in their survival, such as to regulate many physiological processes like, metabolism, cell development, cell proliferation, protein synthesis, translation, and cell death; autophagy. One main sensor for nutrient sensing in Saccharomyces cerevisiae is the target of rapamycin (TOR) pathway. TOR monitors both intra and extracellular factors and incorporates nutrient signals with physiological signals to control its downstream effector
Like TORC1, Gnc2 (general control nonderepressible 2) is a kinase that is activated by an uncharged tRNA that accumulates when amino acid levels are reduced. When Gnc2 is activated by uncharged tRNAs, Gnc2 phosphorylates and inhibits eIF2α (eukaryotic initiation factor- 2α) causing protein synthesis repression in response to stress conditions, converting it to inhibit the eIF2B (guanine nuclear exchange factor of eIF2). When eIF2b is inactivated it represses protein translation by trapping eIF2 in its GDP bound state2. In the presence of low nutrients, cells will try to make amino acids, try to break down proteins so that they can restore the concentration of amino acids and try to pump out any stored amino acids out of the vacuoles/lysosome into cytoplasm while blocking
In depleted nutrient conditions, autophagy is stimulated for survival. Not only is TOR a nutrient sensor that controls cell growth, it also controls autophagy in yeast. Yeast TORC1 regulates autophagy by inhibiting protein kinase Atg1 by phosphorylating Atg13 and preventing Atg13 from interacting with Atg1, Atg17, Atg29, and Atg31, resulting in the inhibition of early activation steps of autophagy1.

In yeast, Whi2 (whiskey 2), a cytoplasmic scaffold protein in Saccharomyces cerevisiae, also play an important role in autophagy4. When mutant whi2 strains are in poor nutrient environments, an overgrowth phenotype is observed due to its down regulating proteins associated in the cell division cycle. Many knock out strains of yeast exhibit similar growth phenotypes like whi2KO when grown on low amino acid media such as leucine.

We know that whi2 is involved in inhibition of growth response- when aa low whi2 turn down cell growth. Whi2 involves in instigation of autophagy- part of a response when cells are being