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Replacement of a conserved tyrosine by tryptophan in Gal3p of Saccharomyces cerevisiae reduces constitutive activity: implications for signal transduction in the GAL regulon

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Abstract

The ability of Saccharomyces cerevisiae to utilize galactose is regulated by the nucleo-cytoplasmic shuttling of a transcriptional repressor, the Gal80 protein. Gal80 interacts with the transcriptional activator Gal4 in the nucleus and inhibits its function, preventing induction of the GAL genes. In response to galactose, the relative amounts of Gal80 in the cytoplasm and the nucleus are modulated by the action of a signal transducer, Gal3. Although it has been speculated that Gal3 binds galactose, this has not been experimentally demonstrated. In this study, we show that replacement of a conserved tyrosine in Gal3 by tryptophan leads to a reduction of its constitutive activity in the absence of galactose. In addition, this mutant protein was fully functional in vivo only when high concentrations of galactose were present in the medium. When overexpressed, the mutant was found to activate the genes GAL1 and GAL7/10 differentially. The implications of these findings for the fine regulation of GAL genes, and its physiological significance, are discussed.

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Acknowledgements

We would like to thank Prof. P. V. Balaji and M. S. Sujatha for their help in preparing the manuscript. We also acknowledge financial support from the Board of Research in Nuclear Sciences, India

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Authors and Affiliations

  1. Laboratory of Molecular Genetics, School of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, 400 076, India

    Anirudha Lakshminarasimhan & Paike Jayadeva Bhat

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  1. Anirudha Lakshminarasimhan
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  2. Paike Jayadeva Bhat
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Correspondence to Anirudha Lakshminarasimhan.

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Communicated by M. Johnston

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Lakshminarasimhan, A., Bhat, P.J. Replacement of a conserved tyrosine by tryptophan in Gal3p of Saccharomyces cerevisiae reduces constitutive activity: implications for signal transduction in the GAL regulon. Mol Genet Genomics 274, 384–393 (2005). https://doi.org/10.1007/s00438-005-0031-6

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  • DOI: https://doi.org/10.1007/s00438-005-0031-6

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