Regulation of Transcription Activation by Gal4p
Karin D. Breunig
Institut für Genetik, Martin-Luther-Universität Halle-Wittenberg, 06099 Halle, Germany
Article history:
Received November 24, 2000
Accepted December 8, 2000
Key words:
Gal4p, transcriptional activity, Saccharomyces cerevisiae
Summary:
Gal4p, a member of a fungal trans-activator family, regulates transcription of genes controlling metabolism of galactose and galactose disaccharides like lactose in yeast. This article reviews recent work on the function and regulation of the Gal4p activation domain. The molecular switch that activates Gal4p in response to galactose consists of two proteins, Gal80p and Gal1p or Gal3p. Gal80p can directly interact with Gal4p and Gal1p/ Gal3p. The latter interaction depends on galactose and ATP and relieves the inhibitory effect of Gal80p on Gal4p. How Gal80p is inactivated by this interaction is unknown. Since the synthesis of Gal80p and Gal1p/Gal3p is under control of Gal4p and the concentration of both proteins is crucial for Gal4p activity, the regulon is entirely under feedback control. On the basis of comparison between homologous regulators from Saccharomyces cerevisiae and Kluyveromyces lactis it is proposed that the dynamics of the intermolecular interactions is important for the transcriptional switch. Differences in the mode of regulation that are observed between the two yeasts are likely to be caused by different kinetic parameters rather than by mechanistic differences. However, the phosphorylation of Gal4p in S. cerevisae and Gal80p in K. lactis suggests that different ways exist to integrate additional signals into the regulon.
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