Ras2 is a ''

Saccharomyces cerevisiae ''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have been o ...

'' 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.

Modifications

Ras2 becomes post-translationally modified in two ways, both being necessary for its activity: Upon activation, palmitoylation at its

C terminus The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...

takes place and causes attachment from the cytoplasm to the plasma membrane. Farnesylation allows for efficient interaction with the downstream

adenylate cyclase Adenylate cyclase (EC 4.6.1.1, also commonly known as adenyl cyclase and adenylyl cyclase, abbreviated AC) is an enzyme with systematic name ATP diphosphate-lyase (cyclizing; 3′,5′-cyclic-AMP-forming). It catalyzes the following reaction: :A ...

Cyr1p. In wild-type yeast deactivated Ras2 is transported to and degraded in the vacuole, a process for which

Whi2 Whi2 or Whiskey 2 is a 55 kDa globular, cytoplasmatic scaffold protein in Saccharomyces cerevisiae, which plays an essential role in stress response pathways, apparently by passing input signals about nutrient availability on to stress responsive el ...

is essential. Disturbing this process leads to Ras2 accumulation at the mitochondrial membrane, a behavior that was not observed before.

Ras2-cAMP-PKA pathway

When activating the adenylate cyclase, Ras2 indirectly raises the cellular

cAMP Camp may refer to: Outdoor accommodation and recreation * Campsite or campground, a recreational outdoor sleeping and eating site * a temporary settlement for nomads * Camp, a term used in New England, Northern Ontario and New Brunswick to descri ...

levels, thereby activating the

PKA PKA may refer to: * Professionally known as: ** Pen name ** Stage persona * p''K''a, the symbol for the acid dissociation constant at logarithmic scale * Protein kinase A, a class of cAMP-dependent enzymes * Pi Kappa Alpha, the North-American so ...

, by which in turn it is downregulated.

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 MSN (meaning Microsoft Network) is a web portal and related collection of Internet services and apps for Windows and mobile devices, provided by Microsoft and launched on August 24, 1995, alongside the release of Windows 95. The Microsoft Net ...

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

References

{{reflist Proteins Saccharomyces cerevisiae genes