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Mol Cell Biol. Jun 1992; 12(6): 2701–2707.
PMCID: PMC364464

Overproduction of the GAL1 or GAL3 protein causes galactose-independent activation of the GAL4 protein: evidence for a new model of induction for the yeast GAL/MEL regulon.


The transcriptional activation function of the Saccharomyces cerevisiae GAL4 protein is modulated by the GAL80 and GAL3 proteins. In the absence of galactose, GAL80 inhibits the function of GAL4, presumably by direct binding to the GAL4 protein. The presence of galactose triggers the relief of the GAL80 block. The key to this relief is the GAL3 protein. How GAL3 and galactose activate GAL4 is not understood, but the long-standing notion has been that a galactose derivative formed by catalytic activity of GAL3 is the inducer that interacts with GAL80 or the GAL80-GAL4 complex. Here we report that overproduction of the GAL3 protein causes constitutive expression of GAL/MEL genes in the absence of exogenous galactose. Overproduction of the GAL1 protein (galactokinase) also causes constitutivity, consistent with the observations that GAL1 is strikingly similar in amino acid sequence to GAL3 and has GAL3-like induction activity. Cells lacking the GAL10-encoded UDP-galactose-UDP-glucose epimerase retained the constitutivity response to overproduction of GAL3, making it unlikely that constitutivity is due to endogenously produced galactose. A galactose-independent mechanism of constitutivity is further indicated by the inducing properties of two newly created galactokinaseless alleles of GAL1. On the basis of these data, we propose a new model for galactose-induced activation of the GAL4 protein. This model invokes galactose-activation of the GAL3 and GAL1 proteins which in turn elicit an alteration of the GAL80-GAL4 complex to activate GAL4. This model is consistent with all the known features of the system and has important implications for manipulating GAL4-dependent transcriptional activation in vitro.

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Selected References

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  • Bajwa W, Torchia TE, Hopper JE. Yeast regulatory gene GAL3: carbon regulation; UASGal elements in common with GAL1, GAL2, GAL7, GAL10, GAL80, and MEL1; encoded protein strikingly similar to yeast and Escherichia coli galactokinases. Mol Cell Biol. 1988 Aug;8(8):3439–3447. [PMC free article] [PubMed]
  • Bhat PJ, Hopper JE. The mechanism of inducer formation in gal3 mutants of the yeast galactose system is independent of normal galactose metabolism and mitochondrial respiratory function. Genetics. 1991 Jun;128(2):233–239. [PMC free article] [PubMed]
  • Bhat PJ, Oh D, Hopper JE. Analysis of the GAL3 signal transduction pathway activating GAL4 protein-dependent transcription in Saccharomyces cerevisiae. Genetics. 1990 Jun;125(2):281–291. [PMC free article] [PubMed]
  • Birnboim HC, Doly J. A rapid alkaline extraction procedure for screening recombinant plasmid DNA. Nucleic Acids Res. 1979 Nov 24;7(6):1513–1523. [PMC free article] [PubMed]
  • Botstein D, Falco SC, Stewart SE, Brennan M, Scherer S, Stinchcomb DT, Struhl K, Davis RW. Sterile host yeasts (SHY): a eukaryotic system of biological containment for recombinant DNA experiments. Gene. 1979 Dec;8(1):17–24. [PubMed]
  • Boyer HW, Roulland-Dussoix D. A complementation analysis of the restriction and modification of DNA in Escherichia coli. J Mol Biol. 1969 May 14;41(3):459–472. [PubMed]
  • Broach JR. Galactose regulation in Saccharomyces cerevisiae. The enzymes encoded by the GAL7, 10, 1 cluster are co-ordinately controlled and separately translated. J Mol Biol. 1979 Jun 15;131(1):41–53. [PubMed]
  • Chasman DI, Kornberg RD. GAL4 protein: purification, association with GAL80 protein, and conserved domain structure. Mol Cell Biol. 1990 Jun;10(6):2916–2923. [PMC free article] [PubMed]
  • Chen EY, Seeburg PH. Supercoil sequencing: a fast and simple method for sequencing plasmid DNA. DNA. 1985 Apr;4(2):165–170. [PubMed]
  • Dagert M, Ehrlich SD. Prolonged incubation in calcium chloride improves the competence of Escherichia coli cells. Gene. 1979 May;6(1):23–28. [PubMed]
  • Hoffman CS, Winston F. A ten-minute DNA preparation from yeast efficiently releases autonomous plasmids for transformation of Escherichia coli. Gene. 1987;57(2-3):267–272. [PubMed]
  • Hopper JE, Broach JR, Rowe LB. Regulation of the galactose pathway in Saccharomyces cerevisiae: induction of uridyl transferase mRNA and dependency on GAL4 gene function. Proc Natl Acad Sci U S A. 1978 Jun;75(6):2878–2882. [PMC free article] [PubMed]
  • Hopper JE, Rowe LB. Molecular expression and regulation of the galactose pathway genes in Saccharomyces cerevisiae. Distinct messenger RNAs specified by the Gali and Gal7 genes in the Gal7-Gal10-Gal1 cluster. J Biol Chem. 1978 Oct 25;253(20):7566–7569. [PubMed]
  • Ito H, Fukuda Y, Murata K, Kimura A. Transformation of intact yeast cells treated with alkali cations. J Bacteriol. 1983 Jan;153(1):163–168. [PMC free article] [PubMed]
  • Johnston M. A model fungal gene regulatory mechanism: the GAL genes of Saccharomyces cerevisiae. Microbiol Rev. 1987 Dec;51(4):458–476. [PMC free article] [PubMed]
  • Johnston SA, Hopper JE. Isolation of the yeast regulatory gene GAL4 and analysis of its dosage effects on the galactose/melibiose regulon. Proc Natl Acad Sci U S A. 1982 Nov;79(22):6971–6975. [PMC free article] [PubMed]
  • Johnston SA, Salmeron JM, Jr, Dincher SS. Interaction of positive and negative regulatory proteins in the galactose regulon of yeast. Cell. 1987 Jul 3;50(1):143–146. [PubMed]
  • Kalckar HM, Kurahashi K, Jordan E. HEREDITARY DEFECTS IN GALACTOSE METABOLISM IN ESCHERICHIA COLI MUTANTS, I. DETERMINATION OF ENZYME ACTIVITIES. Proc Natl Acad Sci U S A. 1959 Dec;45(12):1776–1786. [PMC free article] [PubMed]
  • Kuo CL, Campbell JL. Cloning of Saccharomyces cerevisiae DNA replication genes: isolation of the CDC8 gene and two genes that compensate for the cdc8-1 mutation. Mol Cell Biol. 1983 Oct;3(10):1730–1737. [PMC free article] [PubMed]
  • Lue NF, Chasman DI, Buchman AR, Kornberg RD. Interaction of GAL4 and GAL80 gene regulatory proteins in vitro. Mol Cell Biol. 1987 Oct;7(10):3446–3451. [PMC free article] [PubMed]
  • Ma J, Ptashne M. The carboxy-terminal 30 amino acids of GAL4 are recognized by GAL80. Cell. 1987 Jul 3;50(1):137–142. [PubMed]
  • Meyer J, Walker-Jonah A, Hollenberg CP. Galactokinase encoded by GAL1 is a bifunctional protein required for induction of the GAL genes in Kluyveromyces lactis and is able to suppress the gal3 phenotype in Saccharomyces cerevisiae. Mol Cell Biol. 1991 Nov;11(11):5454–5461. [PMC free article] [PubMed]
  • Nogi Y. GAL3 gene product is required for maintenance of the induced state of the GAL cluster genes in Saccharomyces cerevisiae. J Bacteriol. 1986 Jan;165(1):101–106. [PMC free article] [PubMed]
  • Nogi Y, Fukasawa T. Functional domains of a negative regulatory protein, GAL80, of Saccharomyces cerevisiae. Mol Cell Biol. 1989 Jul;9(7):3009–3017. [PMC free article] [PubMed]
  • Parthun MR, Jaehning JA. Purification and characterization of the yeast transcriptional activator GAL4. J Biol Chem. 1990 Jan 5;265(1):209–213. [PubMed]
  • Ptashne M. How gene activators work. Sci Am. 1989 Jan;260(1):40–47. [PubMed]
  • Rymond BC, Zitomer RS, Schümperli D, Rosenberg M. The expression in yeast of the Escherichia coli galK gene on CYC1::galK fusion plasmids. Gene. 1983 Nov;25(2-3):249–262. [PubMed]
  • Sanger F, Nicklen S, Coulson AR. DNA sequencing with chain-terminating inhibitors. Proc Natl Acad Sci U S A. 1977 Dec;74(12):5463–5467. [PMC free article] [PubMed]
  • Torchia TE, Hopper JE. Genetic and molecular analysis of the GAL3 gene in the expression of the galactose/melibiose regulon of Saccharomyces cerevisiae. Genetics. 1986 Jun;113(2):229–246. [PMC free article] [PubMed]
  • Tsuyumu S, Adams BG. Dilution kinetic studies of yeast populations: in vivo aggregation of galactose utilizing enzymes and positive regulator molecules. Genetics. 1974 Jul;77(3):491–505. [PMC free article] [PubMed]
  • Wu HC, Kalckar HM. Endogenous induction of the galactose operon in Escherichia coli K12. Proc Natl Acad Sci U S A. 1966 Mar;55(3):622–629. [PMC free article] [PubMed]
  • Yun SJ, Hiraoka Y, Nishizawa M, Takio K, Titani K, Nogi Y, Fukasawa T. Purification and characterization of the yeast negative regulatory protein GAL80. J Biol Chem. 1991 Jan 15;266(2):693–697. [PubMed]

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