Department of Biochemistry and Molecular Biology, IMBW, BioCentrum Amsterdam, Vrije Universiteit, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands1
Author for correspondence: Willem H. Mager. Tel: +31 20 444 7569. Fax: +31 20 444 7553. e-mail: mager{at}chem.vu.nl
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Keywords: glucose repression, signal transduction, protein kinase A (PKA), glucose 6-phosphate, HSP12
Abbreviations: FGM, fermentable growth medium (pathway); PKA, protein kinase A; STRE, stress-responsive element
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
We have studied expression levels of the general stress-responsive gene HSP12 under various growth conditions. This gene, encoding a small heat-shock protein, is expressed under conditions of high osmolarity, heat shock and oxidative stress, during nutrient limitation (Praekelt & Meacock, 1990 ; Varela et al., 1995
) and during growth on non-fermentable carbon sources (Siderius et al., 1997
). The transcriptional regulators Msn2p and Msn4p are involved in the activation of HSP12 expression during stress conditions (Martinez-Pastor et al., 1996
). These factors have been shown to shuttle between cytosol and nucleus in conditions allowing normal growth, and to accumulate in the nucleus in stress conditions and under circumstances of low protein kinase A (PKA) activity (Gorner et al., 1998
). Msn2p and Msn4p bind to stress-responsive elements (STREs) that are present in the promoter of many stress-responsive genes (Moskvina et al., 1998
) and mediate transcriptional activation of these genes. The promoter of the HSP12 gene contains five of these elements, which have been shown to be involved in transcriptional regulation under different stress conditions (Varela et al., 1995
; Siderius et al., 1997
).
We have studied repression of HSP12 expression under conditions in which the growth potential of the cell increases, by performing carbon-source-shift experiments. Cells growing on a non-fermentable carbon source contain a high level of HSP12 mRNA (Siderius et al., 1997 ), which is rapidly diminished when glucose is added to the culture.
Glucose-dependent repression of many genes is regulated via the main glucose-repression pathway. This signalling route is involved in repression of genes involved in the use of alternative carbon sources, and of gluconeogenic genes (Ronne, 1995 ; Gancedo, 1998
). A binding site for the transcription factor Mig1p is present in the promoter of these genes (Nehlin et al., 1991
; Lundin et al., 1994
). This factor binds to a complex of co-repressors containing Ssn6p and Tup1p, and the total complex confers glucose repression (Treitel & Carlson, 1995
).
During the transition from vegetative growth to fermentation, the activation of PKA results in adaptive changes in enzyme activities and gene expression (Thevelein, 1994 ). PKA is a multisubunit protein kinase consisting of a pair of regulatory subunits encoded by BCY1 and a pair of catalytic subunits redundantly encoded by TPK1, TPK2 and TPK3 (Thevelein, 1994
). Addition of glucose to a non-fermenting yeast culture results in activation of adenylate cyclase, causing a rapid increase in the cellular level of cAMP. This compound binds to the regulatory subunit of PKA, thereby releasing and activating the catalytic subunits. It is still unclear by what mechanism addition of glucose causes activation of adenylate cyclase. It has been proposed that Ras2p is involved in this process (Jiang et al., 1998
). New evidence has shed some doubt on this (Colombo et al., 1998
), since it was shown that not Ras2p but rather the G-protein
-subunit Gpa2p and the G-protein-coupled receptor Gpr1p are involved in the increase in cellular cAMP after glucose addition (Yun et al., 1998
; Kraakman et al., 1999
). Ras2p may be indirectly involved in glucose activation of PKA since it mediates activation of adenylate cyclase upon the intracellular acidification that occurs after addition of sugar to yeast cells (Colombo et al., 1998
).
An alternative way of activating PKA, independent of the cellular cAMP level, has been described; this pathway is called the fermentable growth medium (FGM) induced pathway (Thevelein, 1991 ; Crauwels et al., 1997
). Phosphorylation of glucose is not required for activation of PKA via this route, in contrast to activation via cAMP (Pernambuco et al., 1996
). The TPK homologue protein kinase Sch9p is believed to play a role in this pathway (Crauwels et al., 1997
).
In the present study, we used mutants defective in several glucose signalling components to investigate which signal transduction routes play a part in the negative regulation of HSP12 expression by low amounts of glucose. In addition, we used reporter constructs containing different regions of the HSP12 promoter to map promoter elements involved in glucose repression.
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
To further investigate the putative role of PKA activity in glucose repression of HSP12, we made use of the wimp mutant (tpk1w1tpk2
tpk3
bcy1), which has a low constitutive level of PKA activity (Cameron et al., 1988
). In a 0·02% glucose-shift experiment, HSP12 levels appeared to drop in this strain as in wild-type cells (Fig. 3a
), confirming that cAMP-dependent activation of PKA is not involved in glucose repression of this gene. This result also indicates that direct activation of the catalytic subunits Tpk2p or Tpk3p, which may occur via the FGM pathway (Crauwels et al., 1997
), is not essential for glucose repression of HSP12.
|
Formation of glucose 6-phosphate is essential for glucose repression of HSP12
A key question in understanding the molecular mechanism underlying repression of HSP12 by low concentrations of glucose is whether glucose acts as a signalling molecule itself or whether it needs to be metabolized to produce the actual signal. Sugar phosphorylation is the first step in glucose metabolism and we found evidence that this step is essential for repression of HSP12. We used a yeast strain in which the genes for all three sugar-phosphorylating enzymes are deleted: hxk1
hxk2
glk1. Addition of glucose to a final concentration of 0·02% did not cause a drop in HSP12 mRNA level in this strain (Fig. 4a
). Moreover, addition of the glucose analogue 6-deoxyglucose, which can be taken up by the yeast cell but cannot be phosphorylated, did not cause HSP12 repression in wild-type cells (Fig. 4b
). These data strongly suggest that formation of glucose 6-phosphate is required for glucose repression of HSP12. However, an alternative interpretation of our findings could be that binding of the substrate glucose to hexokinase may induce a regulatory function of this protein. Indeed, a regulatory role for Hxk2p has been postulated previously (De Winde et al., 1996
; Herrero et al., 1998
; Randezgil et al., 1998
). Therefore, we aimed to confirm the importance of sugar phosphorylation for signalling, by using a strain in which both HXK1 and HXK2 are deleted. The kinase still present, Glk1p, can phosphorylate glucose, but not fructose. Addition of a low amount of glucose to a
hxk1
hxk2 strain caused repression of HSP12 (Fig. 4c
), whereas addition of the same amount of fructose did not (Fig. 4d
). These data support our hypothesis that formation of glucose 6-phosphate and not the activity of Hxk2p is essential for HSP12 repression by low glucose concentrations.
|
It could be argued that the effect of the pgi1 mutation on glucose signalling is due to the inability to form trehalose 6-phosphate (from glucose 6-phosphate) rather than the lack of glucose 6-phosphate itself. Therefore we examined a mutant with a TPS1 deletion. In fact, we used a
tps1
hxk2 double mutant, since a
tps1 mutant rapidly dies on glucose unless hexokinase activity is decreased (Hohmann et al., 1993
). Addition of glucose to this
tps1
hxk2 strain caused repression of HSP12 to the same level as in the wild-type (data not shown).
Taken together, the results of these experiments led us to conclude that formation of glucose 6-phosphate, but no further metabolism into glycolysis, is essential for the observed repression of HSP12 by low amounts of glucose. So far it is unknown how this metabolite may mediate signal transmission in yeast.
Msn2p and Msn4p do not play a role in glucose repression of HSP12
In order to link the role of glucose 6-phosphate as a mediator of repression to a possible control region in the HSP12 promoter, we investigated whether known transcriptional regulators binding to this promoter might be involved in this process. Transcriptional activation of general stress-responsive genes is mediated by the transcriptional regulators Msn2p and Msn4p, which bind to STREs (Martinez-Pastor et al., 1996 ; Schmitt & McEntee, 1996
). In the HSP12 promoter five such STREs are present (Varela et al., 1995
). Under conditions of low PKA activity, Msn2/4p are mainly present in the nucleus, in contrast to conditions where PKA activity is high. We assumed therefore that Msn2/4p are present in the nucleus during growth on glycerol and translocate to the cytosol when glucose is added, which might cause the drop in HSP12 expression. To test this idea, 0·02% glucose was added to a glycerol-grown culture of a
msn2
msn4 strain. Surprisingly, this strain displayed normal expression of HSP12 during growth on glycerol and, moreover, glucose addition caused normal repression of HSP12 (Fig. 5
). These data indicate that Msn2/4p are dispensable for the carbon-source-dependent regulation of HSP12 expression.
|
In order to discriminate between the possibilities that glucose addition might affect turnover of HSP12 mRNA or transcription of the HSP12 gene, we analysed HSP12-promoterGUS fusion constructs. Fusion of the HSP12 promoter and the GUS reporter has occurred at the ATG so that all fusion genes contain only the leader sequence of the HSP12 gene. Thus, if upon glucose addition post-transcriptional regulation occurs, we would expect the same effect on different fusion-gene mRNAs, irrespective of the promoter region present in the respective constructs. We compared the glucose regulation of the fusion gene containing the full promoter (KV3GUS, see Fig. 6) with
31GUS, in which a truncated fragment of the HSP12 promoter, containing no known transcriptional regulatory elements, was fused to a GUS-reporter gene. Expression of the
31 reporter gene appeared not to be subject to glucose repression, whereas the KV3GUS construct displayed the same regulatory characteristics as the HSP12 gene itself (Fig. 7a
, b
). Thus, we can conclude that the drop in HSP12 mRNA level after addition of glucose is not caused by post-transcriptional regulation, but is accomplished by a transcriptional repression.
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Addition of very low amounts of glucose (0·02%) to non-fermenting yeast cells appeared to cause rapid repression of HSP12 and induction of RPS28A expression. Repression by low concentrations of glucose has previously also been demonstrated for the gluconeogenic genes FBP1 and PCK1 (Yin et al., 1996 ). Apparently, even a very low amount of glucose is perceived by yeast cells as a growth-triggering signal. We have shown that phosphorylation of the sugar, but no further metabolism into glycolysis, is required for signalling to HSP12 gene expression. The data supporting this conclusion are that (i) glucose does not cause HSP12 repression in a
hxk1
hxk2
glk1 strain, (ii) fructose does not give rise to HSP12 repression in a
hxk1
hxk2 strain, (iii) 6-deoxyglucose has no repressive effect, and (iv) fructose does not lead to repression in a
pgi1 strain. It is likely therefore that glucose 6-phosphate serves at the signalling molecule, as was shown previously for the gluconeogenic genes FBP1 and PCK1 (Yin et al., 1996
). However, we cannot exclude the possibility that formation of another non-glycolytic metabolite is involved in repression of HSP12 (Gonçalves & Planta, 1998
).
Previously, partial repression of stress-responsive genes such as CTT1 and SSA3 has been shown to occur after addition of 2% fructose to hxk1
hxk2 cells, suggesting that formation of glucose 6-phosphate is not essential (Pernambuco et al., 1996
). We consider it likely that the difference with our data has to do with the final sugar concentration used. Glucose (or fructose) in fermentable amounts may be sensed through the glucose receptor Gpr1p, which activates the adenylate cyclase pathway via Gpa2p (Kraakman et al., 1999
). Kraakman et al. (1999)
observed repression of HSP12 to be delayed in a
gpr1 or
gpa2 strain. However, we found repression of HSP12 by low amounts of glucose to be unaffected in
gpr1 or
gpa2 strains. We have not further analysed repression by fermentable amounts of sugar and we are not able to discriminate whether signal transduction under these conditions might be composed of both types of glucose signalling.
The low amounts of glucose causing HSP12 repression, as well as the results obtained with the mig1 and
ssn6 mutants, indicate that the main glucose-repression pathway does not play a role. In addition, evidence was obtained that neither cAMP-dependent activation of PKA, nor cAMP-independent activation of Tpk2p or Tpk3p, underlies the signalling by low amounts of glucose. We cannot exclude the possibility that the activity of Tpk1p (wimp) is modulated under these experimental conditions.
Unexpectedly, the transcription factors Msn2p and Msn4p, which play a predominant part in transcriptional activation of HSP12 under stress conditions (Varela et al., 1995 ), are not implicated in glucose repression of this gene. This finding fits with the negative results concerning the effect of PKA, since activity of Msn2/4p is largely determined by the cellular PKA activity (Gorner et al., 1998
). The level of derepression of HSP12 in glycerol-grown cells is similar in the
msn2
msn4 strain as compared to the wild-type. This raises the question, presently under study, how activation (derepression) of HSP12 in yeast growing on a non-fermentable carbon source occurs.
Given the fact that Msn2/4p are dispensable for repression of HSP12 by low glucose concentrations, it is even more surprising that an STRE in the promoter of HSP12 may be the target of this regulation. By making use of HSP12-promoter fusion genes the repression phenomenon could be demarcated to a proximal promoter region between -234 and -228, where an STRE is located. Although the rapid decrease in GUS-mRNA after glucose addition occurred similarly for the KV3GUS and 32GUS constructs, a clear difference could be observed at later time points. This phenomenon needs to be investigated further. We consider it likely that this difference reflects the different promoter regions present in the respective constructs, which may be important for sustained repression or resumption of activation. Note that the KV3GUS construct contains three distal STREs, which may also play a role in glucose repression of HSP12.
Our results suggest that an as yet unidentified factor mediates transcriptional repression of HSP12 by glucose. We have preliminary evidence, obtained by bandshift analyses, that such an STRE-binding factor, distinct from Msn2/4p, indeed exists. Other workers have reported discrepancies between the effect of STRE deletions and disruption of MSN2/MSN4 (Ni & LaPorte, 1995 ; Parrou et al., 1999
). It remains to be elucidated if these findings also reflect the action of (a) novel STRE-binding factor(s).
![]() |
ACKNOWLEDGEMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Boles, E., Heinisch, J. & Zimmermann, F. K. (1993). Different signals control the activation of glycolysis in the yeast Saccharomyces cerevisiae.Yeast 9, 761-770.[Medline]
Cameron, S., Levin, L., Zoller, M. & Wigler, M. (1988). cAMP-independent control of sporulation, glycogen metabolism, and heat shock resistance in S. cerevisiae.Cell 53, 555-566.[Medline]
Cereghino, G. P. & Scheffler, I. E. (1996). Genetic analysis of glucose regulation in Saccharomyces cerevisiae: control of transcription versus mRNA turnover.EMBO J 15, 363-374.[Abstract]
Colombo, S., Ma, P. S., Cauwenberg, L. & 8 other authors (1998). Involvement of distinct G-proteins, Gpa2 and Ras, in glucose- and intracellular acidification-induced cAmp signalling in the yeast Saccharomyces cerevisiae. EMBO J 17, 33263341.
Corominas, J., Clotet, J., Fernandez-Banares, I., Boles, E., Zimmermann, F. K., Guinovart, J. J. & Arino, J. (1992). Glycogen metabolism in a Saccharomyces cerevisiae phosphoglucose isomerase (pgil) disruption mutant.FEBS Lett 310, 182-186.[Medline]
Crauwels, M., Donaton, M. C. V., Pernambuco, M. B., Winderickx, J., De Winde, J. H. & Thevelein, J. M. (1997). The Sch9 protein kinase in the yeast Saccharomyces cerevisiae controls cApk activity and is required for nitrogen activation of the fermentable-growth-medium-induced (FGM) pathway.Microbiology 143, 2627-2637.[Abstract]
De Winde, J. H., Crauwels, M., Hohmann, S., Thevelein, J. M. & Winderickx, J. (1996). Differential requirement of the yeast sugar kinases for sugar sensing in establishing the catabolite-repressed state.Eur J Biochem 241, 633-643.[Abstract]
Estruch, F. & Carlson, M. (1993). Two homologous zinc finger genes identified by multicopy suppression in a SNF1 protein kinase mutant of Saccharomyces cerevisiae.Mol Cell Biol 13, 3872-3881.[Abstract]
Gancedo, J. M. (1998). Yeast carbon catabolite repression.Microbiol Mol Biol Rev 62, 334-361.
Gonçalves, P. & Planta, R. J. (1998). Starting up yeast glycolysis.Trends Microbiol 6, 314-319.[Medline]
Gorner, W., Durchschlag, E., Martinez-Pastor, M. T., Estruch, F., Ammerer, G., Hamilton, B., Ruis, H. & Schuller, C. (1998). Nuclear localization of the C2H2 zinc finger protein Msn2p is regulated by stress and protein kinase A activity.Genes Dev 12, 586-597.
Griffioen, G., Mager, W. H. & Planta, R. J. (1994). Nutritional upshift response of ribosomal protein gene transcription in Saccharomyces cerevisiae.FEMS Microbiol Lett 123, 137-144.[Medline]
Griffioen, G., Laan, R. J., Mager, W. H. & Planta, R. J. (1996). Ribosomal protein gene transcription in Saccharomyces cerevisiae shows a biphasic response to nutritional changes.Microbiology 142, 2279-2287.[Abstract]
Herrero, P., Martinezcampa, C. & Moreno, F. (1998). The hexokinase 2 protein participates in regulatory DNAprotein complexes necessary for glucose repression of the SUC2 gene in Saccharomyces cerevisiae.FEBS Lett 434, 71-76.[Medline]
Hohmann, S. (1997). Shaping up: the responses of yeast to osmotic stress. In Yeast Stress Responses, pp. 101146. Edited by S. Hohmann & W. H. Mager. Georgetown, TX: R. G. Landes.
Hohmann, S., Neves, M. J., de Koning, W., Alijo, R., Ramos, J. & Thevelein, J. M. (1993). The growth and signalling defects of the ggs1 (fdp1/byp1) deletion mutant on glucose are suppressed by a deletion of the gene encoding hexokinase PII.Curr Genet 23, 281-289.[Medline]
Jiang, Y., Davis, C. & Broach, J. R. (1998). Efficient transition to growth on fermentable carbon sources in Saccharomyces cerevisiae requires signaling through the Ras pathway.EMBO J 17, 6942-6951.
Kraakman, L., Lemaire, K., Ma, P. S., Teunissen, A., Donaton, M. C. V., Van Dijck, P., Winderickx, J., de Winde, J. H. & Thevelein, J. M. (1999). A Saccharomyces cerevisiae G-protein coupled receptor, Gpr1, is specifically required for glucose activation of the cAMP pathway during the transition to growth on glucose.Mol Microbiol 32, 1002-1012.[Medline]
Kubler, E., Mosch, H. U., Rupp, S. & Lisanti, M. P. (1997). Gpa2p, a G-protein alpha-subunit, regulates growth and pseudohyphal development in Saccharomyces cerevisiae via a cAMP-dependent mechanism.J Biol Chem 272, 20321-20323.
Lombardo, A., Cereghino, G. P. & Scheffler, I. E. (1992). Control of mRNA turnover as a mechanism of glucose repression in Saccharomyces cerevisiae.Mol Cell Biol 12, 2941-2948.[Abstract]
Lorenz, M. C. & Heitman, J. (1997). Yeast pseudohyphal growth is regulated by Gpa2, a G protein alpha homolog.EMBO J 16, 7008-7018.
Lundin, M., Nehlin, J. O. & Ronne, H. (1994). Importance of a flanking AT-rich region in target site recognition by the GC box-binding zinc finger protein MIG1.Mol Cell Biol 14, 1979-1985.[Abstract]
Mager, W. H. & Planta, R. J. (1991). Coordinate expression of ribosomal protein genes in yeast as a function of cellular growth rate.Mol Cell Biochem 104, 181-187.[Medline]
Martinez-Pastor, M. T., Marchler, G., Schuller, C., Marchler-Bauer, A., Ruis, H. & Estruch, F. (1996). The Saccharomyces cerevisiae zinc finger proteins Msn2p and Msn4p are required for transcriptional induction through the stress response element (STRE).EMBO J 15, 2227-35.[Abstract]
Meijer, M. M. C., Boonstra, J., Verkleij, A. J. & Verrips, C. T. (1998). Glucose repression in Saccharomyces cerevisiae is related to the glucose concentration rather than the glucose flux.J Biol Chem 273, 24102-24107.
Moskvina, E., Schuller, C., Maurer, C. T., Mager, W. H. & Ruis, H. (1998). A search in the genome of Saccharomyces cerevisiae for genes regulated via stress response elements.Yeast 14, 1041-1050.[Medline]
Nehlin, J. O., Carlberg, M. & Ronne, H. (1991). Control of yeast GAL genes by MIG1 repressor: a transcriptional cascade in the glucose response.EMBO J 10, 3373-3377.[Abstract]
Ni, H. T. & LaPorte, D. C. (1995). Response of a yeast glycogen synthase gene to stress.Mol Microbiol 16, 1197-1205.[Medline]
Nonet, M., Scafe, C., Sexton, J. & Young, R. (1987). Eucaryotic RNA polymerase conditional mutant that rapidly ceases mRNA synthesis.Mol Cell Biol 7, 1602-1611.[Medline]
Ozcan, S., Vallier, L. G., Flick, J. S., Carlson, M. & Johnston, M. (1997). Expression of the SUC2 gene of Saccharomyces cerevisiae is induced by low levels of glucose.Yeast 13, 127-137.[Medline]
Parrou, J. L., Enjalbert, B., Plourde, L., Bauche, A., Gonzalez, B. & Francois, J. (1999). Dynamic responses of reserve carbohydrate metabolism under carbon and nitrogen limitations in Saccharomyces cerevisiae.Yeast 15, 191-203.[Medline]
Pernambuco, M. B., Winderickx, J., Crauwels, M., Griffioen, G., Mager, W. H. & Thevelein, J. M. (1996). Glucose-triggered signalling in Saccharomyces cerevisiae: different requirements for sugar phosphorylation between cells grown on glucose and those grown on non-fermentable carbon sourcesMicrobiology 142, 1775-1782.[Abstract]
Praekelt, U. M. & Meacock, P. A. (1990). HSP12, a new small heat shock gene of Saccharomyces cerevisiae: analysis of structure, regulation and function.Mol Gen Genet 223, 97-106.[Medline]
Randezgil, F., Sanz, P., Entian, K. D. & Prieto, J. A. (1998). Carbon source-dependent phosphorylation of hexokinase PII and its role in the glucose-signaling response in yeast.Mol Cell Biol 18, 2940-2948.
Ronne, H. (1995). Glucose repression in fungi.Trends Genet 11, 12-17.[Medline]
Scheffler, I. E., Delacruz, B. J. & Prieto, S. (1998). Control of mRNA turnover as a mechanism of glucose repression in Saccharomyces cerevisiae.Int J Biochem Cell Biol 30, 1175-1193.[Medline]
Schmitt, A. P. & McEntee, K. (1996). Msn2p, a zinc finger DNA-binding protein, is the transcriptional activator of the multistress response in Saccharomyces cerevisiae.Proc Natl Acad Sci USA 93, 5777-5782.
Siderius, M., Rots, E. & Mager, W. H. (1997). High-osmolarity signalling in Saccharomyces cerevisiae is modulated in a carbon-source-dependent fashion.Microbiology 143, 3241-3250.[Abstract]
Thevelein, J. M. (1991). Fermentable sugars and intracellular acidification as specific activators of the RASadenylate cyclase signalling pathway in yeast: the relationship to nutrient-induced cell cycle control.Mol Microbiol 5, 1301-1307.[Medline]
Thevelein, J. M. (1994). Signal transduction in yeast.Yeast 10, 1753-1790.[Medline]
Thomas, B. J. & Rothstein, R. (1989). Elevated recombination rates in transcriptionally active DNA.Cell 56, 619-630.[Medline]
Toda, T., Uno, I., Ishikawa, T. & 7 other authors (1985). In yeast, RAS proteins are controlling elements of adenylate cyclase. Cell 40, 2736.[Medline]
Treitel, M. A. & Carlson, M. (1995). Repression by SSN6TUP1 is directed by MIG1, a repressor/activator protein.Proc Natl Acad Sci USA 92, 3132-3136.[Abstract]
Varela, J. C., Praekelt, U. M., Meacock, P. A., Planta, R. J. & Mager, W. H. (1995). The Saccharomyces cerevisiae HSP12 gene is activated by the high-osmolarity glycerol pathway and negatively regulated by protein kinase A.Mol Cell Biol 15, 6232-6245.[Abstract]
Yin, Z. K., Smith, R. J. & Brown, A. J. P. (1996). Multiple signalling pathways trigger the exquisite sensitivity of yeast gluconeogenic mRNAs to glucose.Mol Microbiol 20, 751-764.[Medline]
Yun, C. W., Tamaki, H., Nakayama, R., Yamamoto, K. & Kumagai, H. (1998). Gpr1p, a putative G-protein coupled receptor, regulates glucose-dependent cellular cAMP level in yeast Saccharomyces cerevisiae.Biochem Biophys Res Commun 252, 29-33.[Medline]
Received 2 September 1999;
revised 18 October 1999;
accepted 17 November 1999.