Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The two regulatory pathways appear to come together at the IME1 gene. It is clearly regulated by mating type and induced by starvation as well. Overexpression of IME1 completely overcomes MAT defects but may not circumvent all nutritional control. Kassir et al. (1988) found that overexpression of IME1 allowed sporulation in the presence of glucose and nitrogen. They also have found a meiotic level of message in temperature-sensitive cdc25 diploids shifted to high temperature in rich medium (Simchen and Kassir, 1989). Smith and Mitchell (1989) found that overexpression of IME1 induced an early meiotic event (recombination) in rich medium, but later meiotic events did not occur (i.e., they detected no spore formation). Mitchell (personal communication) has suggested that the difference may be due to differences in the amount of nitrogen present in the two experiments. Thus, while it is clear that IME1 is a necessary positive regulator of meiosis, responding both to mating type and nutritional conditions, it is not clear if it is sufficient. It is possible that other genes are involved in the response to starvation. One interpretation is that a separate nutritional control is exerted for events starting with meiosis I. Much of the regulatory pathway that allows yeast cells to enter meiosis has been determined. As in the case in many sensory transduction pathways, the initial signal for starvation is not yet known, nor is the nature of the proposed downstream phosphorylated effector. Given the power of yeast molecular genetics, answers to both these questions seem attainable. Another area that remains unclear is the difference between responses to nitrogen starvation versus carbon source. Many of the experiments discussed above do not address this question. The strategies used by yeast may be utilized in the developmental decisions used by other, more complex eukaryotes. Certainly several of the gene products involved in nutritional control in yeast have homologies in mammalian systems. For example, the human H-ras gene can substitute for yeast RAS; the relationship is sufficiently close that dominant Ha-ras mutations that inhibit CDC25 have been found (Powers et al., 1989). Furthermore, these dominant Ha-ras mutations have the appropriate phenotype in mammalian cells, suggesting the presence of a CDC25-like protein. Although the major components of mating type control appear to have been defined, the mechanism of the RME1-IME transcriptional control remains to be determined.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Dual regulation of meiosis in yeast. 218 88

Entry into meiosis in Saccharomyces cerevisiae cells is regulated by starvation through the adenylate cyclase/cAMP-dependent protein kinase (AC/PK) pathway. The gene IME1 is also involved in starvation control of meiosis. Multicopy IME1 plasmids overcome the meiotic deficiency of bcy1 and of RASval19 diploids. Double mutants ime1 cdc25 and ime1 ras2 are sporulation deficient. These results suggest that IME1 comes after the AC/PK cascade. Furthermore, the level of IME1 transcripts is affected by mutations in the AC/PK genes CDC25, CYR1 and BCY1. Moreover, the addition of cAMP to a cyr1-2 diploid suppresses IME1 transcription. The presence in a bcy1 diploid of IME1 multicopy plasmids does not cure the failure of bcy1 cells to arrest as unbudded cells following starvation and to enter the G0 state (thermotolerance, synthesis of unique G0 proteins). This indicates that the pathway downstream of the AC/PK cascade branches to control meiosis through IME1, and to control entry into G0 and cell cycle initiation, independently of IME1.
 ...
PMID:The adenylate cyclase/protein kinase cascade regulates entry into meiosis in Saccharomyces cerevisiae through the gene IME1. 220 44

A mutation in the gene IRA1 (formerly called PPD1) was originally characterized as a deficiency of a phosphoprotein phosphatase. The IRA1 gene has been cloned and sequenced. A large open reading frame (8,817 base pairs) which can encode a protein of 2,938 amino acids was found. Northern (RNA) blot analysis detected a message of about 10 kilobases, and nuclease S1 protection demonstrated mRNA start points at 97 and 98 base pairs upstream from the putative initiator ATG codon. Disruption of the IRA1 gene resulted in sensitivity to nitrogen starvation and heat shock. Diploids homozygous for the disrupted IRA1 gene were deficient in sporulation. Disruption of the IRA1 gene suppressed the lethality of the cdc25 mutation but did not suppress the lethality of either the ras1 ras2 or the cyr1 mutations. Deficiency of the phosphoprotein phosphatase was not reproducible in the disruption mutant of the IRA1 gene. Moreover, the ira1 mutant showed an increased level of cyclic AMP. Our results suggest that the IRA1 protein inhibits the function of the RAS proteins in a fashion antagonistic to the function of the CDC25 protein in the RAS-cyclic AMP pathway in Saccharomyces cerevisiae.
 ...
PMID:IRA1, an inhibitory regulator of the RAS-cyclic AMP pathway in Saccharomyces cerevisiae. 254 Apr 26

The plasma-membrane ATPase of Saccharomyces cerevisiae is a proton pump whose activity, essential fro proliferation, is subject to regulation by nutritional signals. The previous finding that the CDC25 gene product is required for the glucose-induced H+-ATPase activation suggested that H+-ATPase activity is regulated by cAMP. Analysis of starvation-induced inactivation and glucose-induced activation of the H+-ATPase in mutants affected in activity of the RAS proteins, adenylyl cyclase or cAMP-dependent protein kinase showed that nutritional regulation of H+-ATPase activity does not depend directly on any of these factors. We conclude that adenlyl cyclase does not mediate all nutritional responses. This also indicates that the specific CDC25 requirement for the glucose-induced activation of the H+-ATPase identifies a new function for the CDC25 gene product, a function that appears to be independent of CDC25-mediated modulation of the RAS/adenylyl cyclase/cAMP pathway.
 ...
PMID:cAMP- and RAS-independent nutritional regulation of plasma-membrane H+-ATPase activity in Saccharomyces cerevisiae. 255 50

Normally, meiosis and sporulation in Saccharomyces cerevisiae occur only in diploid strains and only when the cells are exposed to starvation conditions. Diploidy is determined by the mating-type system (the genes MAT, RME1, IME1), whereas the starvation signal is transmitted through the adenylate cyclase - protein kinase pathway (the genes CDC25, RAS2, CDC35 (CYR1), BCY1, TPK1, TPK2, TPK3). The two regulatory pathways converge at the gene IME1, which is a positive regulator of meiosis and whose early expression in sporulating cells correlates with the initiation of meiosis. Sites upstream (5') of IME1 appear to mediate in the repression of the gene by repressors originating from both the mating-type and the cyclase--kinase pathways.
 ...
PMID:Genetic regulation of differentiation towards meiosis in the yeast Saccharomyces cerevisiae. 268 11

The CDC25 gene product is a guanine nucleotide exchange factor for Ras proteins in yeast. Recently it has been suggested that the intracellular levels of guanine nucleotides may influence the exchange reaction. To test this hypothesis we measured the levels of nucleotides in yeast cells under different growth conditions and the relative amount of Ras2-GTP. The intracellular GTP/GDP ratio was found to be very sensitive to growth conditions: the ratio is high, close to that of ATP/ADP during exponential growth, but it decreases rapidly before the beginning of stationary phase, and it drops further under starvation conditions. The addition of glucose to glucose-starved cells causes a fast increase of the GTP/GDP ratio. The relative amount of Ras2-GTP changes in a parallel way suggesting that there is a correlation with the cytosolic GTP/GDP ratio. In addition 'in vitro' mixed-nucleotide exchange experiments done on purified Ras2 protein demonstrated that the GTP and GDP concentrations influence the extent of Ras2-GTP loading giving further support to their possible regulatory role.
 ...
PMID:Role of guanine nucleotides in the regulation of the Ras/cAMP pathway in Saccharomyces cerevisiae. 1133 89

To isolate the CDC25 gene of Saccharomyces cerevisiae we have transformed a cdc25-1, trp1 strain with a yeast gene bank constructed in YRp7 vector, selecting trp clones able to grow at restrictive temperature. From several independent positive clones we have recovered a plasmid, called pDGEm-1, that bears a 5-kb genomic fragment and is able to give a full complementation of the cdc25-1 mutation. The genomic sequence has been subcloned and a good complementation obtained with a 2-kb fragment. Several stable integrative trp, cdc transformants have been constructed. Their genetic and molecular analysis indicates that we have cloned the true CDC25 gene. Northern blot hybridization has revealed the presence of a 5-kb mRNA transcribed by the CDC25 gene. This mRNA is also present in nitrogen-starved cells and during the re-enter in cell cycle from starvation, suggesting a constitutive transcription. Transformants bearing the cloned sequence on multicopy plasmid and integrative transformants that bear the CDC25 gene, flanked by plasmid sequences, show an altered control of the cell cycle and fail to arrest in G1 unbudded phase in stationary phase conditions.
 ...
PMID:Molecular cloning and transcriptional analysis of the start gene CDC25 of Saccharomyces cerevisiae. 1645 7