Ras2
Ras2 is a Saccharomyces cerevisiae guanine nucleotide-binding protein (encoded by the RAS2 gene) which becomes activated by binding GTP when glucose is present in the environment. It affects growth regulation and starvation response.{{cite web |title=RAS2/YNL098C Protein Information |url=https://www.yeastgenome.org/locus/S000005042 |work=Saccharomyces Genome Database |accessdate=4 January 2012}}
Modifications
Ras2 becomes post-translationally modified in two ways, both being necessary for its activity: Upon activation, palmitoylation at its C terminus takes place and causes attachment from the cytoplasm to the plasma membrane. Farnesylation allows for efficient interaction with the downstream adenylate cyclase Cyr1p.{{cite journal |jstor=2367245 |bibcode=1995PNAS...92.2984B |doi=10.1073/pnas.92.7.2984 |pmid=7708760 |title=Ras Membrane Targeting is Essential for Glucose Signaling but not for Viability in Yeast |year=1995 |last1=Bhattacharya |first1=Sharmila |journal=Proceedings of the National Academy of Sciences |volume=92 |issue=7 |pages=2984–8 |last2=Chen |first2=Li |last3=Broach |first3=James R. |last4=Powers |first4=Scott |pmc=42343|doi-access=free }} In wild-type yeast deactivated Ras2 is transported to and degraded in the vacuole, a process for which Whi2 is essential. Disturbing this process leads to Ras2 accumulation at the mitochondrial membrane, a behavior that was not observed before.{{cite journal |pmid=19208759 |year=2009 |last1=Leadsham |first1=Jane E. |last2=Miller |first2=Katherine |last3=Ayscough |first3=Kathryn R. |last4=Colombo |first4=Sonia |last5=Martegani |first5=Enzo |last6=Sudbery |first6=Pete |last7=Gourlay |first7=Campbell W. |title=Whi2 links nutritional sensing to actin-dependent Ras-cAMP-PKA regulation and apoptosis in yeast |volume=122 |issue=5 |pages=706–15 |doi=10.1242/jcs.042424 |pmc=2720921 |journal=Journal of Cell Science}}
Ras2-cAMP-PKA pathway
When activating the adenylate cyclase, Ras2 indirectly raises the cellular cAMP levels, thereby activating the PKA, by which in turn it is downregulated.{{cite journal |pmid=21457714 |year=2011 |last1=Dong |first1=Jian |last2=Bai |first2=Xiaojia |title=The membrane localization of Ras2 and the association between Cdc25p and Ras2-GTP are regulated by protein kinase A (PKA) in the yeast Saccharomyces cerevisiae |volume=585 |issue=8 |pages=1127–34 |doi=10.1016/j.febslet.2011.03.057 |journal=FEBS Letters|s2cid=27110 |doi-access=free }}
Downstream effects
In a probably indirect manner via the above PKA regulation, Ras2 has a suppressing effect on the yeast general stress response transcription factor Msn2.{{cite journal |pages=3127–38 |doi=10.1091/mbc.E10-12-1007 |title=Fine-tuning of the Msn2/4-mediated yeast stress responses as revealed by systematic deletion of Msn2/4 partners |year=2011 |last1=Sadeh |first1=Amit |last2=Movshovich |first2=Natalia |last3=Volokh |first3=Misha |last4=Gheber |first4=Larisa |last5=Aharoni |first5=Amir |journal=Molecular Biology of the Cell |volume=22 |issue=17 |pmid=21757539 |pmc=3164460}}
Active Ras2 was also found in the nucleus, the reason is currently unknown.{{Citation needed|date=January 2012}}