Disease relevance of RAS2

• The E. coli transformant carrying the yeast RAS2 or RAS2val19 gene had no adenylate cyclase activity [1].
• The RAS2 gene is consistently required for maintenance of life span when heat stress is chronic or in its extension when heat stress is transient or absent altogether [2].
• In addition, activation of Ras2, a regulator of cAMP generation, results in some protection from fluconazole toxicity in a fashion independent of the efflux transporter Pdr5p [3].

High impact information on RAS2

• The yeast ERI1 gene encodes a small ER-localized protein that associates in vivo with GTP bound Ras2 in an effector loop-dependent manner [4].
• Functional cloning of BUD5, a CDC25-related gene from S. cerevisiae that can suppress a dominant-negative RAS2 mutant [5].
• Adenylyl cyclase activity in membranes from cells that lacked CAP was not stimulated by RAS2 proteins in vitro [6].
• The TPK1 gene carried on a multicopy plasmid can suppress both a temperature-sensitive ras2 gene and adenylate cyclase gene [7].
• In contrast to the S. cerevisiae RAS1 and RAS2 gene products, the YPT protein seems to be involved, directly or indirectly, in microtubule organization and function [8].

Biological context of RAS2

• We present a genetic analysis of RAS1 and RAS2 of S. cerevisiae, two genes that are highly homologous to mammalian ras genes [9].
• By constructing in vitro ras genes disrupted by selectable genes and introducing these by gene replacement into the respective ras loci, we have determined that neither RAS1 nor RAS2 are by themselves essential genes [9].
• S. cerevisiae strains containing RAS2val19, a RAS2 gene with a missense mutation analogous to one that activates the transforming potential of mammalian ras genes, have growth and biochemical properties strikingly similar to yeast strains carrying IAC or bcy1 [10].
• TS1 cells accumulate as unbudded cells upon temperature shift from 30 to 37 degrees C, thus showing that the RAS1 and RAS2 gene functions are important for progression through the G1 phase of the cell cycle [11].
• The yeast RAS1 and RAS2 genes appear to be involved in control of cell growth in response to nutrients [12].

Anatomical context of RAS2

• Overexpression of the budding yeast RAS2 gene in Nicotiana plumbaginifolia cells revealed that RAS2 acted as 'suicide' gene in freshly isolated protoplasts from leaves and blocked cell proliferation in cell suspension-derived protoplasts [13].
• Ras2 proteins expressed in an erf2Delta strain have a reduced level of palmitoylation and are partially mislocalized to the vacuole [14].
• Erf2p has been shown to be required for the plasma membrane localization of GFP-Ras2p via a pathway distinct from the classical secretory pathway (X. Dong and R. J. Deschenes, manuscript in preparation) [15].
• The possible mechanisms of ASC1/RAS2 suppression of atp1-2 are discussed; we suggest that RAS2 is part of the regulatory circuit involved in the control of F(1)-ATPase subunit levels in mitochondria [16].
• Mutants in the Saccharomyces cerevisiae RAS2 gene influence life span, cytoskeleton, and regulation of mitosis [17].

Associations of RAS2 with chemical compounds

• Production of cAMP in the transformant carrying CYR1 and either RAS2 or RAS2val19 was confirmed by staining colonies on maltose-MacConkey plates and by measuring induction of beta-galactosidase by isopropyl beta-D-thiogalactopyranoside [1].
• Activating mutations (valine 19 or leucine 68) were introduced into the Saccharomyces cerevisiae RAS1 and RAS2 genes [18].
• This enzyme activity, detected by using a synthetic peptide sequence based on the C-terminus of a ras protein, may be responsible not only for the essential methylation of the farnesyl cysteine residue of a mating factor, but also for the methylation of yeast RAS1 and RAS2 proteins and possibly other polypeptides with similar C-terminal structures [19].
• One of these suppressors was a mutated RAS2 gene in which the transition C/G----T/A at position 455 resulted in replacement of threonine 152 by isoleucine in the protein [20].
• This activity of RAS2 is effected by the cyclic AMP pathway [21].

Physical interactions of RAS2

• On the basis of these data, we propose that the ability of Cdc25 to interact with Ras2 proteins is strongly dependent on the activation state of Ras2 [22].
• Like the wild-type enzyme, the RAS-dependent activity of the mutant adenylate cyclase is turned on by the GTP-bound form of the RAS2 protein [11].
• These results strongly suggest that the residues R80 and N81 are situated in or closely associated with the Ras2p specific site binding Sdc25p [23].

Enzymatic interactions of RAS2

• Ste24p cleaves the carboxyl-terminal "-AAX" from the yeast mating pheromone a-factor, whereas Rce1p cleaves the -AAX from both a-factor and Ras2p [24].

Regulatory relationships of RAS2

• Screening of approximately 13,000 mutagenized colonies for galactose-dependent growth at a high temperature (37 degrees) yielded six temperature-sensitive ras2 (ras2ts) mutations and one temperature-sensitive cyr1 (cyr1ts) mutation that can be suppressed by overexpression or increased dosage of RAS2 [25].
• The binding properties of Cdc25 to Ras2 were strongly diminished in yeast cells expressing an inactive Ira1 protein, which normally acts as a negative regulator of Ras activity [22].
• To isolate temperature-sensitive mutations in the RAS2 gene, we constructed a plasmid carrying a RAS2 gene whose expression is under the control of the galactose-inducible GAL1 promoter [25].
• Cells carrying a high copy number of plasmid GPA2 (YEpGPA2) had markedly elevated levels of cAMP and could suppress a temperature-sensitive mutation of RAS2 [26].
• Partially purified preparations of the carboxy-terminal domain of the SCD25 gene product enhanced the exchange rate of guanosine diphosphate (GDP) to guanosine triphosphate (GTP) of pure RAS2 protein by stimulating the release of GDP [27].

Other interactions of RAS2

• A GPA2 null allele conferred a severe growth defect on cells containing a null allele of RAS2, although either mutation alone had little effect on growth rate [12].
• Genetic data suggest that the yeast cell cycle control gene CDC25 is an upstream regulator of RAS2 [22].
• Strains lacking ERF2 are viable, but they have a synthetic growth defect in the absence of RAS2 and partially suppress the heat shock sensitivity resulting from expression of the hyperactive RAS2(V19) allele [14].
• We tested whether SHR5, like previously isolated suppressors of hyperactivated RAS2, acts by affecting the membrane attachment and/or posttranslational modification of Ras proteins [28].
• We have previously demonstrated that STE14 encodes the enzyme which mediates carboxyl methylation of the Saccharomyces cerevisiae CAAX proteins a-factor, RAS1, and RAS2 [29].

Analytical, diagnostic and therapeutic context of RAS2

• The replicative life span of Saccharomyces cerevisiae was previously shown to be modulated by the homologous signal transducers Ras1p and Ras2p in a reciprocal manner [21].
• Here, we show by northern blot and reporter gene (beta-galactosidase) assays that deletion of genes encoding Tor1p and Ras2p resulted in increased PRX1 expression, indicating that these proteins are also mediators of the glucose repression effect [30].
• Tester strains were subsequently used for the reintroduction of various combinations of wild-type and mutated RAS2 and CDC25 genes by genetic techniques, as well as for in vitro reconstitution assays with the corresponding proteins [31].
• Sequence analysis revealed that ASC1 was allelic with RAS2, a G-protein growth regulator [16].
• Mst50 also interacts with Ras1, Ras2, Cdc42, and Mgb1 in yeast two-hybrid assays [32].

References