scholarly journals RAG4 Gene Encodes a Glucose Sensor in Kluyveromyces lactis

Genetics ◽  
2001 ◽  
Vol 158 (2) ◽  
pp. 541-548
Author(s):  
Svätopluk Betina ◽  
Paola Goffrini ◽  
Iliana Ferrero ◽  
Micheline Wésolowski-Louvel
Keyword(s):  
Glucose Transporter ◽  
Glucose Sensor ◽  
Glucose Repression ◽  
Kluyveromyces Lactis ◽  
Glucose Sensing ◽  
Dual Function ◽  
Wild Type ◽  
Transporter Family ◽  
Low Concentrations ◽  
High Concentrations

Abstract The rag4 mutant of Kluyveromyces lactis was previously isolated as a fermentation-deficient mutant, in which transcription of the major glucose transporter gene RAG1 was affected. The wild-type RAG4 was cloned by complementation of the rag4 mutation and found to encode a protein homologous to Snf3 and Rgt2 of Saccharomyces cerevisiae. These two proteins are thought to be sensors of low and high concentrations of glucose, respectively. Rag4, like Snf3 and Rgt2, is predicted to have the transmembrane structure of sugar transporter family proteins as well as a long C-terminal cytoplasmic tail possessing a characteristic 25-amino-acid sequence. Rag4 may therefore be expected to have a glucose-sensing function. However, the rag4 mutation was fully complemented by one copy of either SNF3 or RGT2. Since K. lactis appears to have no other genes of the SNF3/RGT2 type, we suggest that Rag4 of K. lactis may have a dual function of signaling high and low concentrations of glucose. In rag4 mutants, glucose repression of several inducible enzymes is abolished.

scholarly journals Rgt1p of Saccharomyces cerevisiae, a key regulator of glucose-induced genes, is both an activator and a repressor of transcription.

1996 ◽  
Vol 16 (11) ◽  
pp. 6419-6426 ◽  
Author(s):  
S Ozcan ◽  
T Leong ◽  
M Johnston
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Glucose Transporter ◽  
Glucose Sensor ◽  
Glucose Sensors ◽  
Hexose Transporter ◽  
Glucose Signaling ◽  
Low Glucose ◽  
Induced Genes ◽  
Low Levels ◽  
High Concentrations

The RGT1 gene of Saccharomyces cerevisiae plays a central role in the glucose-induced expression of hexose transporter (HXT) genes. Genetic evidence suggests that it encodes a repressor of the HXT genes whose function is inhibited by glucose. Here, we report the isolation of RGT1 and demonstrate that it encodes a bifunctional transcription factor. Rgt1p displays three different transcriptional modes in response to glucose: (i) in the absence of glucose, it functions as a transcriptional repressor; (ii) high concentrations of glucose cause it to function as a transcriptional activator; and (iii) in cells growing on low levels of glucose, Rgt1p has a neutral role, neither repressing nor activating transcription. Glucose alters Rgt1p function through a pathway that includes two glucose sensors, Snf3p and Rgt2p, and Grr1p. The glucose transporter Snf3p, which appears to be a low-glucose sensor, is required for inhibition of Rgt1p repressor function by low levels of glucose. Rgt2p, a glucose transporter that functions as a high-glucose sensor, is required for conversion of Rgt1p into an activator by high levels of glucose. Grr1p, a component of the glucose signaling pathway, is required both for inactivation of Rgt1p repressor function by low levels of glucose and for conversion of Rgt1p into an activator at high levels of glucose. Thus, signals generated by two different glucose sensors act through Grr1p to determine Rgt1p function.

The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis

1993 ◽  
Vol 13 (7) ◽  
pp. 3882-3889
Author(s):  
C Prior ◽  
P Mamessier ◽  
H Fukuhara ◽  
X J Chen ◽  
M Wesolowski-Louvel
Keyword(s):  
Glucose Transporter ◽  
Kinase Activity ◽  
Glucose Repression ◽  
Kluyveromyces Lactis ◽  
Transport Systems ◽  
Transporter Gene ◽  
Rag1 Gene ◽  
Sugar Kinase

The RAG1 gene of Kluyveromyces lactis encodes a low-affinity glucose/fructose transporter. Its transcription is induced by glucose, fructose, and several other sugars. The RAG4, RAG5, and RAG8 genes are trans-acting genes controlling the expression of the RAG1 gene. We report here the characterization of one of these genes, RAG5. The nucleotide sequence of the cloned RAG5 gene indicated that it encodes a protein that is homologous to hexokinases of Saccharomyces cerevisiae. rag5 mutants showed no detectable hexokinase or glucokinase activity, suggesting that the sugar kinase activity encoded by this gene is the only hexokinase in K. lactis. Both high- and low-affinity transport systems of glucose were affected in rag5 mutants. The defect of the low-affinity component was found to be due to a block of transcription of the RAG1 gene by the hexokinase mutation. In vivo complementation of the rag5 mutation by the HXK2 gene of S. cerevisiae and complementation of hxk1 hxk2 mutations of S. cerevisiae by the RAG5 gene showed that RAG5 and HXK2 were equivalent for sugar-phosphorylating activity but that RAG5 could not restore glucose repression in the S. cerevisiae hexokinase mutants.

Yeast actin with a subdomain 4 mutation (A204C) exhibits increased pointed-end critical concentration

2007 ◽  
Vol 85 (3) ◽  
pp. 319-325 ◽  
Author(s):  
David J. Teal ◽  
John F. Dawson
Keyword(s):  
Actin Polymerization ◽  
Critical Concentration ◽  
Structural Studies ◽  
Wild Type ◽  
Low Concentrations ◽  
Engineering Strategy ◽  
High Concentrations ◽  
Pointed End ◽  
Very High

Characterizing mutants of actin that do not polymerize will advance our understanding of the mechanism of actin polymerization and will be invaluable for the production of short F-actin structures for structural studies. To circumvent the problem of expressing dominant lethal nonpolymerizing actin in yeast, we adopted a cysteine engineering strategy. Here we report the characterization of a mutant of yeast actin, AC-actin, possessing a single pointed-end mutation, A204C. Expression of this mutant in yeast results in actin-polymerization-deficient phenotypes. When copolymerized with wild-type actin, ATP–AC-actin is incorporated into filaments. ADP–AC-actin participates in the nucleation and elongation of wild-type filaments only at very high concentrations. At low concentrations, ADP–AC-actin appears to participate only in the nucleation of wild-type filaments, suggesting that Ala-204 is involved in modulating the critical concentration of the pointed end of actin.

Biofilm Growth of Escherichia coli Is Subject to cAMP-Dependent and cAMP-Independent Inhibition

2015 ◽  
Vol 25 (2-3) ◽  
pp. 209-225 ◽  
Author(s):  
Sarah L. Sutrina ◽  
Kia Daniel ◽  
Michael Lewis ◽  
Naomi T. Charles ◽  
Cherysa K.E. Anselm ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Catabolite Repression ◽  
Ph Effects ◽  
Wild Type ◽  
Inhibitory Effects ◽  
Phosphotransferase System ◽  
Biofilm Growth ◽  
E Coli ◽  
Low Concentrations ◽  
High Concentrations

We established that <i>Escherichia coli </i>strain 15 (ATCC 9723) produces both curli and cellulose, and forms robust biofilms. Since this strain is wild type with respect to the phosphoenolpyruvate:sugar phosphotransferase system (PTS), it is an ideal strain in which to investigate the effects of the PTS on the biofilm growth of <i>E. coli</i>. We began by looking into the effects of PTS and non-PTS sugars on the biofilm growth of this strain. All the sugars tested tended to activate biofilm growth at low concentrations but to inhibit biofilm growth at high concentrations. Acidification of the medium was an inhibitory factor in the absence of buffer, but buffering to prevent a pH drop did not prevent the inhibitory effects of the sugars. The concentration at which inhibition set in varied from sugar to sugar. For most sugars, cyclic (c)AMP counteracted the inhibition at the lowest inhibitory concentrations but became ineffective at higher concentrations. Our results suggest that cAMP-dependent catabolite repression, which is mediated by the PTS in <i>E. coli</i>, plays a role in the regulation of biofilm growth in response to sugars. cAMP-independent processes, possibly including Cra, also appear to be involved, in addition to pH effects.

Protease-activated receptors 1 and 4 mediate thrombin signaling in endothelial cells

Blood ◽  
2003 ◽  
Vol 102 (9) ◽  
pp. 3224-3231 ◽  
Author(s):  
Hiroshi Kataoka ◽  
Justin R. Hamilton ◽  
David D. McKemy ◽  
Eric Camerer ◽  
Yao-Wu Zheng ◽  
...  
Keyword(s):  
Endothelial Cells ◽  
Wild Type ◽  
Protease Activated Receptors ◽  
Erk Phosphorylation ◽  
Low Concentrations ◽  
Extracellular Signal ◽  
High Concentrations ◽  
Mouse Aorta

AbstractDefining the relative importance of protease-activated receptors (PARs) for thrombin signaling in mouse endothelial cells is critical for a basic understanding of thrombin signaling in these cells and for the rational use of knockout mice to probe the roles of thrombin's actions on endothelial cells in vivo. We examined thrombin- and PAR agonist–induced increases in cytoplasmic calcium, phosphoinositide hydrolysis, extracellular signal-regulated kinase (ERK) phosphorylation, and gene expression in endothelial cells from wild-type and PAR-deficient mice. PAR1 and PAR4 agonists triggered responses in wild-type but not in Par1–/– and Par4–/– endothelial cells, respectively. Calcium imaging confirmed that a substantial fraction of individual endothelial cells responded to both agonists. Compared with wild-type cells, Par1–/– endothelial cells showed markedly decreased responses to low concentrations of thrombin, and cells that lacked both PAR1 and PAR4 showed no responses to even high concentrations of thrombin. Similar results were obtained when endothelial-dependent vasorelaxation of freshly isolated mouse aorta was used as an index of signaling in native endothelial cells. Thus PAR1 is the major thrombin receptor in mouse endothelial cells, but PAR4 also contributes. These receptors serve at least partially redundant roles in endothelial cells in vitro and in vivo and together are necessary for the thrombin responses measured.

Isolation and characterization of rat skeletal myoblast mutants resistant to lectins

1983 ◽  
Vol 3 (12) ◽  
pp. 2166-2171
Author(s):  
B Gilfix ◽  
J Rogers ◽  
B D Sanwal
Keyword(s):  
Wheat Germ Agglutinin ◽  
Wheat Germ ◽  
Wild Type ◽  
Skeletal Myoblast ◽  
Skeletal Myoblasts ◽  
Isolation And Characterization ◽  
Low Concentrations ◽  
High Concentrations ◽  
Made In

Mutants resistant to the lethal action of the lectins phytohemagglutinin A (PHA) and wheat germ agglutinin (WGA) have been made in a line of differentiating rat skeletal myoblasts. The WGA mutants are of two types, WGArII, resistant to low concentrations of the lectin, and WGArI, resistant to high concentrations of the lectin. WGArII and PHAr mutants are unable to differentiate, whereas WGArI mutants differentiate normally. WGArII mutants are not impaired in the binding of wheat germ agglutinin, but WGArI mutants bind the lectin only to the extent of about 50% of the wild-type values. All of the mutants are cross-resistant to lectins other than those used in their selection.

Salicylate inhibits the translation and transcription of ompF in Escherichia coli

2001 ◽  
Vol 47 (11) ◽  
pp. 1053-1057 ◽  
Author(s):  
Nat Ramani ◽  
Kwaku Boakye
Keyword(s):  
Escherichia Coli ◽  
Membrane Protein ◽  
Outer Membrane Protein ◽  
Mrna Levels ◽  
Strong Inhibition ◽  
Wild Type ◽  
High Osmolarity ◽  
Number Of Factors ◽  
Low Concentrations ◽  
High Concentrations

OmpF is a major outer membrane protein in Escherichia coli whose expression is regulated by a large number of factors, including the osmolarity of the growth medium and the concentration of salicylate. We have previously shown that at low osmolarity, OmpF is post-transcriptionally regulated by micF mRNA, and that at high osmolarity, regulation occurs primarily by the inhibition of transcription by OmpR (Ramani et al. 1994). In contrast, salicylate was reported to alter OmpF expression solely by blocking translation primarily through micF mRNA (Rosner et al. 1991). We examined the effect of salicylate by analyzing the levels of OmpF in wild-type and micF– strains grown with salicylate. At low concentrations of salicylate (0–4 mM), OmpF levels were inhibited strongly in wild-type cells, whereas no inhibition of OmpF was observed in the micF– strain. At high concentrations of salicylate (10–20 mM), both the wild type and the micF– strain showed strong inhibition of OmpF. To study the effect of salicylate on transcription, ompF mRNA and micF mRNA were analyzed in wild-type cells. micF mRNA levels increased during growth with 1, 2, and 4 mM salicylate. In contrast, ompF mRNA levels were not affected by low concentrations of salicylate, but decreased strongly at 10 and 20 mM salicylate. Taken together, these results suggest that similar to osmoregulation, salicylate inhibits both the translation and transcription of ompF.Key words: salicylate, OmpF, micF, osmoregulation.

scholarly journals Characterization of KlGRR1 and SMS1 Genes, Two New Elements of the Glucose Signaling Pathway of Kluyveromyces lactis

2008 ◽  
Vol 7 (8) ◽  
pp. 1299-1308 ◽  
Author(s):  
Martina Hnatova ◽  
Micheline Wésolowski-Louvel ◽  
Guenaëlle Dieppois ◽  
Julien Deffaud ◽  
Marc Lemaire
Keyword(s):  
Signaling Pathway ◽  
Glucose Transporter ◽  
Glucose Sensor ◽  
Kluyveromyces Lactis ◽  
Single Gene ◽  
Negative Regulator ◽  
Casein Kinase I ◽  
Glucose Signaling ◽  
F Box Protein

ABSTRACT The expression of the major glucose transporter gene, RAG1, is induced by glucose in Kluyveromyces lactis. This regulation involves several pathways, including one that is similar to Snf3/Rgt2-ScRgt1 in Saccharomyces cerevisiae. We have identified missing key components of the K. lactis glucose signaling pathway by comparison to the same pathway of S. cerevisiae. We characterized a new mutation, rag19, which impairs RAG1 regulation. The Rag19 protein is 43% identical to the F-box protein ScGrr1 of S. cerevisiae and is able to complement an Scgrr1 mutation. In the K. lactis genome, we identified a single gene, SMS1 (for similar to Mth1 and Std1), that encodes a protein showing an average of 50% identity with Mth1 and Std1, regulators of the ScRgt1 repressor. The suppression of the rag4 (glucose sensor), rag8 (casein kinase I), and rag19 mutations by the Δsms1 deletion, together with the restoration of RAG1 transcription in the double mutants, demonstrates that Sms1 is a negative regulator of RAG1 expression and is acting downstream of Rag4, Rag8, and Rag19 in the cascade. We report that Sms1 regulates KlRgt1 repressor activity by preventing its phosphorylation in the absence of glucose, and that SMS1 is regulated by glucose, both at the transcriptional and the posttranslational level. Two-hybrid interactions of Sms1 with the glucose sensor and KlRgt1 repressor suggest that Sms1 mediates the glucose signal from the plasma membrane to the nucleus. All of these data demonstrated that Sms1 was the K. lactis homolog of MTH1 and STD1 of S. cerevisiae. Interestingly, MTH1 and STD1 were unable to complement a Δsms1 mutation.

scholarly journals The hexokinase gene is required for transcriptional regulation of the glucose transporter gene RAG1 in Kluyveromyces lactis.

1993 ◽  
Vol 13 (7) ◽  
pp. 3882-3889 ◽  
Author(s):  
C Prior ◽  
P Mamessier ◽  
H Fukuhara ◽  
X J Chen ◽  
M Wesolowski-Louvel
Keyword(s):  
Glucose Transporter ◽  
Kinase Activity ◽  
Glucose Repression ◽  
Kluyveromyces Lactis ◽  
Transport Systems ◽  
Transporter Gene ◽  
Rag1 Gene ◽  
Sugar Kinase

The RAG1 gene of Kluyveromyces lactis encodes a low-affinity glucose/fructose transporter. Its transcription is induced by glucose, fructose, and several other sugars. The RAG4, RAG5, and RAG8 genes are trans-acting genes controlling the expression of the RAG1 gene. We report here the characterization of one of these genes, RAG5. The nucleotide sequence of the cloned RAG5 gene indicated that it encodes a protein that is homologous to hexokinases of Saccharomyces cerevisiae. rag5 mutants showed no detectable hexokinase or glucokinase activity, suggesting that the sugar kinase activity encoded by this gene is the only hexokinase in K. lactis. Both high- and low-affinity transport systems of glucose were affected in rag5 mutants. The defect of the low-affinity component was found to be due to a block of transcription of the RAG1 gene by the hexokinase mutation. In vivo complementation of the rag5 mutation by the HXK2 gene of S. cerevisiae and complementation of hxk1 hxk2 mutations of S. cerevisiae by the RAG5 gene showed that RAG5 and HXK2 were equivalent for sugar-phosphorylating activity but that RAG5 could not restore glucose repression in the S. cerevisiae hexokinase mutants.

Mechanism of glucose sensing in the small intestine

2003 ◽  
Vol 31 (6) ◽  
pp. 1140-1142 ◽  
Author(s):  
J. Dyer ◽  
S. Vayro ◽  
S.P. Shirazi-Beechey
Keyword(s):  
Glucose Transporter ◽  
Glucose Sensor ◽  
Cell Function ◽  
Glucose Sensing ◽  
Model Systems ◽  
Luminal Membrane ◽  
Sense And Respond ◽  
Vitro Model

Sensing nutrients is a fundamental task for all living cells. For most eukaryotic cells glucose is a major source of energy, having significant and varied effects on cell function. Interest in identifying mechanisms by which cells sense and respond to variations in glucose concentration has increased recently. The epithelial cells lining the intestinal tract are exposed, from the luminal domain, to an environment with continuous and massive fluctuations in the levels of dietary monosaccharides. Enterocytes therefore have to sense and respond to the significant changes in the levels of luminal sugars, and regulate the expression of the intestinal glucose transporter (Na+/glucose co-transporter, SGLT1) accordingly. Our data, using a combination of in vivo and in vitro model systems, suggest that glucose in the lumen of the intestine is sensed by a glucose sensor residing on the external face of the enterocyte luminal membrane. Glucose binds to the sensor and generates an intracellular signal leading to enhancement in the expression of SGLT1. The generated signal is independent of glucose metabolism and is likely to operate via a G-protein-coupled receptor and cAMP/protein kinase A signalling cascade.

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