Ras2 Explained

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.^[1]

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.^[2] 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.^[3]

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.^[4]

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.^[5]

Active Ras2 was also found in the nucleus, the reason is currently unknown.

Notes and References

1. Web site: RAS2/YNL098C Protein Information . . 4 January 2012.
2. 2367245 . 1995PNAS...92.2984B . 10.1073/pnas.92.7.2984 . 7708760 . Ras Membrane Targeting is Essential for Glucose Signaling but not for Viability in Yeast . 1995 . Bhattacharya . Sharmila . Proceedings of the National Academy of Sciences . 92 . 7 . 2984–8 . Chen . Li . Broach . James R. . Powers . Scott . 42343. free .
3. 19208759 . 2009 . Leadsham . Jane E. . Miller . Katherine . Ayscough . Kathryn R. . Colombo . Sonia . Martegani . Enzo . Sudbery . Pete . Gourlay . Campbell W. . Whi2 links nutritional sensing to actin-dependent Ras-cAMP-PKA regulation and apoptosis in yeast . 122 . 5 . 706–15 . 10.1242/jcs.042424 . 2720921 . Journal of Cell Science.
4. 21457714 . 2011 . Dong . Jian . Bai . Xiaojia . 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 . 585 . 8 . 1127–34 . 10.1016/j.febslet.2011.03.057 . FEBS Letters. 27110 . free .
5. 3127–38 . 10.1091/mbc.E10-12-1007 . Fine-tuning of the Msn2/4-mediated yeast stress responses as revealed by systematic deletion of Msn2/4 partners . 2011 . Sadeh . Amit . Movshovich . Natalia . Volokh . Misha . Gheber . Larisa . Aharoni . Amir . Molecular Biology of the Cell . 22 . 17 . 21757539 . 3164460.