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 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 levels, thereby activating the
PKA, 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.
Active Ras2 was also found in the nucleus, the reason is currently unknown.
References
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Proteins
Saccharomyces cerevisiae genes