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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Schizosaccharomyces pombe initiates sexual development in response to nutritional starvation. The level of cAMP in S. pombe cells changed during the transition from exponential growth to stationary phase. It also changed in response to a shift from nitrogen-rich medium to nitrogen-free medium. A decrease of approximately 50% was observed in either case, suggesting that S. pombe cells contain less cAMP when they initiate sexual development. S. pombe cells that expressed the catalytic domain of Saccharomyces cerevisiae adenylyl cyclase from the S. pombe adh1 promoter contained 5 times as much cAMP as the wild type and could not initiate mating and meiosis. These observations, together with previous findings that exogenously added cAMP inhibits mating and meiosis and that cells with little cAMP are highly derepressed for sexual development, strongly suggest that cAMP functions as a key regulator of sexual development in S. pombe. The pde1 gene, which encodes a protein homologous to S. cerevisiae cAMP phosphodiesterase I, was isolated as a multicopy suppressor of the sterility caused by a high cAMP level. Disruption of pde1 made S. pombe cells partially sterile and meiosis-deficient, indicating that this cAMP phosphodiesterase plays an important role in balancing the cAMP level in vivo.
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PMID:Reduction in the intracellular cAMP level triggers initiation of sexual development in fission yeast. 131 97

The Schizosaccharomyces pombe gpa2 gene was cloned by hybridization with a cDNA for Dictyostelium discoideum G alpha 1. It encodes a homolog of G-protein alpha-subunits with 354 amino acids and a predicted molecular mass of 40,522. Disruption of gpa2 slows cell growth but is not lethal. Cells defective in gpa2 mate and sporulate readily in the presence of plentiful nutrition, bypassing the requirement of nitrogen starvation for the initiation of sexual development. These phenotypes mimic those of cells defective in cyr1 encoding adenylyl cyclase. The level of cAMP in gpa2 null mutants is only one-third of the wild-type level. Mutations in gpa2 that are likely to inhibit the GTPase activity of the gene product cause a slight increase in intracellular cAMP levels and result in leaky sterility. The cAMP level reaches 20 times as high as the wild-type level if a cell carries both this type of gpa2 mutation and a null mutation in pde1 encoding phosphodiesterase. Cells defective in gpa2 fail to produce cAMP in response to glucose stimulation. These results suggest that Gpa2 is involved in the determination of the cAMP level according to nutritional conditions, most likely as a positive regulator of adenylyl cyclase.
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PMID:Characterization of a fission yeast gene, gpa2, that encodes a G alpha subunit involved in the monitoring of nutrition. 134 Apr 62

Disruption of the cyr1 gene of Schizosaccharomyces pombe, which encodes adenylyl cyclase, did not confer lethality to fission yeast cells, although they grew 40% slower than wild-type strains in complete medium. These cells contained no measurable amount of cAMP and no adenylyl cyclase activity. When h+ and h- cyr1 disruptants were mixed, they underwent mating even in rich medium. Propagation of homothallic cyr1 disruptants was difficult, probably because such cells readily mate and produce asci and thus stop growing. A greater than 10-fold increase in the amount of cyr1 mRNA was observed when cloned cyr1+ was introduced into Sch. pombe cells on a multicopy plasmid. The total adenylyl cyclase activity was similarly high in these transformants. However, the level of intracellular cAMP was hardly affected. Evidence suggests that this was not due to increased phosphodiesterase activity. Thus, cAMP level in growing fission yeast cells appears to be regulated not by the amount of adenylyl cyclase protein but by a feedback mechanism at the enzyme level. The cAMP level fell by approximately 50% under nitrogen starvation, which triggers sexual development in Sch. pombe. We suggest that fission yeast controls the level of intracellular cAMP primarily to regulate sexual development rather than to drive or arrest the cell cycle.
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PMID:Adenylyl cyclase is dispensable for vegetative cell growth in the fission yeast Schizosaccharomyces pombe. 217 64

Adenylyl cyclase from S. cerevisiae contains at least two subunits, a 200 kd catalytic subunit and a subunit with an apparent molecular size of 70 kd, which we now call CAP (cyclase-associated protein). We cloned a cDNA encoding CAP by screening a yeast cDNA expression library in E. coli with antisera raised against the purified protein. The cDNA contained an open reading frame capable of encoding a 526 amino acid protein that is not homologous to any sequences in the current data bases. Adenylyl cyclase activity in membranes from cells that lacked CAP was not stimulated by RAS2 proteins in vitro. These results suggest that CAP is required for at least some aspects of the RAS-responsive signaling system. Mutants lacking CAP had four additional phenotypes that appear to be unrelated to effects of the RAS/adenylyl cyclase pathway: the inability to grow on rich medium (YPD), temperature sensitivity on minimal medium, sensitivity to nitrogen starvation, and a swollen cell morphology.
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PMID:Cloning and characterization of CAP, the S. cerevisiae gene encoding the 70 kd adenylyl cyclase-associated protein. 218 42

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.
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PMID:cAMP- and RAS-independent nutritional regulation of plasma-membrane H+-ATPase activity in Saccharomyces cerevisiae. 255 50

When the fission yeast Schizosaccharomyces pombe is starved for nitrogen, the cells are arrested in the G1 phase, enter the G0 phase and initiate sexual development. The ste13 mutant, however, fails to undergo a G1 arrest when starved for nitrogen and since this mutant phenotype is not suppressed by a mutation in adenylyl cyclase (cyr1), it would appear that ste13+ either acts independently of the decrease in the cellular cAMP level induced by starvation for nitrogen, or functions downstream of this controlling event. We have used functional complementation to clone the ste13+ gene from an S. pombe genomic library and show that its disruption is not lethal, indicating that, while the gene is required for sexual development, it is not essential for cell growth. Nucleotide sequencing predicts that ste13+ should encode a protein of 485 amino acids in which the consensus motifs of ATP-dependent RNA helicases of the DEAD box family are completely conserved. Point mutations introduced into these consensus motifs abolished the ste13+ functions. The predicted Ste13 protein is 72% identical to the Drosophila melanogaster Me31B protein over a stretch of 391 amino acids. ME31B is a developmentally regulated gene that is expressed preferentially in the female germline and may be required for oogenesis. Expression of ME31B cDNA in S. pombe suppresses the ste13 mutation. These two evolutionarily conserved genes encoding putative RNA helicases may play a pivotal role in sexual development.
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PMID:The ste13+ gene encoding a putative RNA helicase is essential for nitrogen starvation-induced G1 arrest and initiation of sexual development in the fission yeast Schizosaccharomyces pombe. 807 73

We have isolated Schizosaccharomyces pombe genes that confer sterility to the fission yeast cell when expressed from a multicopy plasmid. One of these genes strongly hybridized to a probe carrying the open reading frame of Saccharomyces cerevisiae TPK1, which encodes a catalytic subunit of the cAMP-dependent protein kinase (protein kinase A). This S. pombe gene, named pka1, has a coding potential of 512 amino acids, and the deduced gene product is 60% identical with the S. cerevisiae Tpk1 protein in the C-terminal 320 amino acids. Disruption of pka1 slows cell growth but is not lethal. The resultant cells, however, are highly derepressed for sexual development, readily undergoing conjugation and sporulation in the absence of nitrogen starvation. They are, thus, phenotypically indistinguishable from the adenylyl cyclase-defective (cyr1-) cells previously characterized, except that the pka1- spores are retarded in germination, whereas the cyr1- spores are not. Disruption of pka1 is epistatic to a defect in cgs1, which encodes the regulatory subunit of protein kinase A. These results strongly suggest that the product of pka1 is a catalytic subunit of protein kinase A and, furthermore, that S. pombe has only one gene encoding it. This situation contrasts with the case of S. cerevisiae, in which three genes encode the catalytic subunits.
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PMID:Cloning of the pka1 gene encoding the catalytic subunit of the cAMP-dependent protein kinase in Schizosaccharomyces pombe. 814 51

Schizosaccharomyces pombe h+ cells secrete a diffusable mating pheromone called P-factor. Here we show that the map2 gene, a defect of which confers h(+)-specific sterility, encodes the precursor of P-factor. We purified P-factor from cells overexpressing map2 and determined its amino acid sequence. P-factor is a peptide of 23 residues, with the sequence Thr-Tyr-Ala-Asp-Phe-Leu-Arg-Ala-Tyr-Gln-Ser- Trp-Asn-Thr-Phe-Val-Asn-Pro-Asp-Arg-Pro-Asn-Leu. A synthetic peptide of this sequence gave the same specific activity and chromatographic profile as the purified P-factor, suggesting that P-factor is unmodified. h- cells starved for nutrition showed a morphological response to P-factor. Transcription of the sxa2 gene, which encodes a protease thought to degrade P-factor, was activated in these cells. The cry1 null mutant, which lacks adenylyl cyclase and has little intracellular cAMP, was susceptible to P-factor even in the presence of nutrients. Combination of the cyr1 and sxa2 mutations enhanced this susceptibility. P-factor induced not only responses toward mating but also arrest of the cell cycle at the G1 phase in h- cyr1 sxa2 cells. This proves that the S. pombe mating pheromone has the ability to arrest cell cycle progression, which has previously been obscured by the usual requirement for mating of nutritional starvation and subsequent growth arrest.
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PMID:The fission yeast mating pheromone P-factor: its molecular structure, gene structure, and ability to induce gene expression and G1 arrest in the mating partner. 831 86

Sporulation in the yeast Saccharomyces cerevisiae occurs in diploid cells following starvation for glucose and nitrogen sources. A key gene in the regulation of the meiotic process is IME1. A well-documented fact is that respiration is necessary for sporulation. We now show that respiration is necessary for the expression of IME1. We suggest that glucose repression of meiosis is transduced through its effect on respiration, in a pathway separate from that of adenylyl cyclase.
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PMID:Mitochondrial activity is required for the expression of IME1, a regulator of meiosis in yeast. 843 51

The Dictyostelium discoideum developmental program is initiated by starvation and its progress depends on G-protein-regulated transmembrane signaling. Disruption of the Dictyostelium G-protein alpha-subunit G alpha 3 (g alpha 3-) blocks development unless the mutant is starved in the presence of artificial cAMP pulses. The function of G alpha 3 was investigated by examining the expression of several components of the cAMP transmembrane signaling system in the g alpha 3- mutant. cAMP receptor 1 protein, cyclic nucleotide phosphodiesterase, phosphodiesterase inhibitor, and aggregation-stage adenylyl cyclase mRNA expression were absent or greatly reduced when cells were starved without exogenously applied pulses of cAMP. However, cAMP receptor 1 protein and aggregation-stage adenylyl cyclase mRNA expression were restored by starving the g alpha 3- cells in the presence of exogenous cAMP pulses. Adenylyl cyclase activity was also reduced in g alpha 3- cells starved without exogenous cAMP pulses compared with similarly treated wild-type cells but was elevated to a level twofold greater than wild-type cells in g alpha 3- cells starved in the presence of exogenous cAMP pulses. These results suggest that G alpha 3 is essential in early development because it controls the expression of components of the transmembrane signaling system.
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PMID:G alpha 3 regulates the cAMP signaling system in Dictyostelium. 930 65


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