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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the absence of the leucine biosynthetic precursor alpha-isopropylmalate (alpha-IPM), the yeast LEU3 protein (Leu3p) binds DNA and acts as a transcriptional repressor in an in vitro extract. Addition of alpha-IPM resulted in a dramatic increase in Leu3p-dependent transcription. The presence of alpha-IPM was also required for Leu3p to compete effectively with another transcriptional activator, GAL4/VP16, for limiting transcription factors. Therefore, the addition of alpha-IPM appears to convert a transcriptional repressor into an activator. This represents an example in eukaryotes of direct transcriptional regulation by a small effector molecule.
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PMID:In vitro transcriptional activation by a metabolic intermediate: activation by Leu3 depends on alpha-isopropylmalate. 143 22

The LEU3 protein of yeast activates a number of genes in the branched chained amino acid pathways. Native LEU3 is modulated by alpha-isopropylmalate, an intermediate in leucine biosynthesis. alpha-Isopropylmalate is needed for transcriptional activation, but not for DNA binding. We show here that the transcriptional activation function of LEU3 resides within the C-terminal 32 amino acids. An adjacent stretch of 81 residues is dispensable and apparently forms a connecting link between the activation domain and a large central region previously identified as important for modulation. The newly defined activation domain contains a cluster of three tryptophan residues, each of which was changed to alanine by site-directed mutagenesis. Surprisingly, all three Trp----Ala mutations affect modulation. One of them, Trp-864----Ala, creates a LEU3 molecule that is largely unmodulated and also is a better transcriptional activator than is wild type LEU3 ("hyperactivator"). The other two mutations (Trp-861----Ala and Trp-870----Ala) change the modulation ratio but have no effect on the maximal activation efficiency of the activator. We propose that the activation domain of LEU3 is kept silent by association with the central region of the protein and that an alpha-isopropylmalate-induced conformational change in the central region releases and thus activates the activation domain.
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PMID:Transcriptional activator LEU3 of yeast. Mapping of the transcriptional activation function and significance of activation domain tryptophans. 221 32

LEU3 of Saccharomyces cerevisiae encodes an 886-amino-acid polypeptide that activates transcription of at least five genes by binding to an upstream decanucleotide sequence. This activation is dependent on the inducer alpha-isopropylmalate, the synthesis of which is repressed by leucine. We created a 285-amino-acid LEU3 derivative by removing a large block of internal sequences, including a dense cluster of acidic residues. This deletion protein bound to the decanucleotide sequence in vitro and activated gene expression in vivo. In contrast to wild-type LEU3, the truncated LEU3 protein was an effective transcriptional activator when alpha-isopropylmalate synthesis was repressed by leucine.
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PMID:A large internal deletion converts yeast LEU3 to a constitutive transcriptional activator. 267 86

The product of the Saccharomyces cerevisiae LEU3 gene, Leu3p, is a transcriptional activator which regulates leucine biosynthesis in response to intracellular levels of leucine through the biosynthetic intermediate alpha-isopropylmalate. We devised a novel assay to examine the DNA site occupancy of Leu3p under different growth conditions, using a reporter gene with internal Leu3p-binding sites. Expression of the reporter is inhibited by binding of nuclear Leu3p to these sites; inhibition is dependent on the presence of the sites in the reporter, on the integrity of the Leu3p DNA-binding domain, and, surprisingly, on the presence of a transcriptional activation domain in the inhibiting protein. By this assay, Leu3p was found to occupy its binding site under all conditions tested, including high and low levels of leucine and in the presence and absence of alpha-isopropylmalate. The localization of Leu3p to the nucleus was confirmed by immunofluorescence staining of cells expressing epitope-tagged Leu3p derivatives. We conclude that Leu3p regulates transcription in vivo without changing its intracellular localization and DNA site occupancy.
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PMID:Detection of leucine-independent DNA site occupancy of the yeast Leu3p transcriptional activator in vivo. 762 98

The Leu3 protein of Saccharomyces cerevisiae binds to specific DNA sequences present in the 5' noncoding region of at least five RNA polymerase II-transcribed genes. Leu3 functions as a transcriptional activator only when the metabolic intermediate alpha-isopropylmalate is also present. In the absence of alpha-isopropylmalate, Leu3 causes transcription to be repressed below basal levels. We show here that different portions of the Leu3 protein are responsible for activation and repression. Fusion of the 30 C-terminal residues of Leu3 to the DNA-binding domain of the Gal4 protein created a strong cross-species activator, demonstrating that the short C-terminal region is not only required but also sufficient for transcriptional activation. Using a recently developed Leu3-responsive in vitro transcription assay as a test system for repression (J. Sze, M. Woontner, J. Jaehning, and G. B. Kohlhaw, Science 258:1143-1145, 1992), we show that mutant forms of the Leu3 protein that lack the activation domain still function as repressors. The shortest repressor thus identified had only about 15% of the mass of the full-length Leu3 protein and was centered on the DNA-binding region of Leu3. Implications of this finding for the mechanism of repression are discussed.
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PMID:Transcriptional regulator Leu3 of Saccharomyces cerevisiae: separation of activator and repressor functions. 835 11

The Leu3 protein of Saccharomyces cerevisiae regulates the expression of genes involved in branched chain amino acid biosynthesis and in ammonia assimilation. It is modulated by alpha-isopropylmalate, an intermediate in leucine biosynthesis. In the presence of alpha-isopropylmalate, Leu3p is a transcriptional activator. In the absence of the signal molecule, the activation domain is masked, and Leu3p acts as a repressor. The recent discovery that Leu3p retains its regulatory properties when expressed in mammalian cells (Guo, H., and Kohlhaw, G. B. (1996) FEBS Lett. 390, 191-195) suggests that masking and unmasking of the activation domain occur without the participation of auxiliary proteins. Here we present experimental support for this notion and address the mechanism of masking. We show that modulation of Leu3p is exceedingly sensitive to mutations in the activation domain. An activation domain double mutant (D872N/D874N; designated Leu3-dd) was constructed that has the characteristics of a permanently masked activator. Using separately expressed segments containing either the DNA binding domain-middle region or the activation domain of wild type Leu3p (or Leu3-dd) in a modified yeast two-hybrid system, we provide direct evidence for alpha-isopropylmalate-dependent interaction between these segments. Finally, we use the phenotype of Leu3-dd-containing cells (slow growth in the absence of added leucine) to select for suppressor mutations that map to the middle region of Leu3-dd. The properties of nine such suppressors further support the idea that masking is an intramolecular process and suggest a means for mapping the surface involved in masking.
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PMID:Evidence that intramolecular interactions are involved in masking the activation domain of transcriptional activator Leu3p. 923 37