Cambridge Systems Biology Centre and Department of Biochemistry, University of Cambridge, Sanger Building, 80 Tennis Court Road, Cambridge CB2 1GA, United Kingdom.
J Biol Chem. 2010 Feb 26;285(9):6465-76. doi: 10.1074/jbc.M109.073288. Epub 2009 Dec 18.
The transcriptional response to environmental changes has to be prompt but appropriate. Previously, it has been shown that the Gis1 transcription factor is responsible for regulating the expression of postdiauxic shift genes in response to nutrient starvation, and this transcription regulation is dependent upon the Rim15 kinase. Here we demonstrate that the activity of Gis1 is negatively modulated by proteasome-mediated limited proteolysis. Limited degradation of Gis1 by the proteasome leads to the production of smaller variants, which have weaker transcription activities than the full-length protein. The coiled-coil domain, absent from the smaller variants, is part of the second transcription activation domain in Gis1 and is essential for both the limited proteolysis of Gis1 and its full activity. Endogenous Gis1 and its variants, regardless of their transcription capabilities, activate transcription in a Rim15-dependent manner. However, when the full-length Gis1 accumulates in cells due to overexpression or inhibition of the proteasome function, transcription activation by Gis1 is no longer solely controlled by Rim15. Together, these data strongly indicate that the function of the limited degradation is to ensure that Gis1-dependent transcription is strictly regulated by the Rim15 kinase. Furthermore, we have revealed that the kinase activity of Rim15 is essential for this regulation.
细胞对环境变化的转录反应必须既迅速又恰当。此前有研究表明，Gis1 转录因子负责调节营养饥饿时的后生代谢转换基因的表达，这种转录调控依赖于 Rim15 激酶。在这里，我们证明 Gis1 的活性受到蛋白酶体介导的有限蛋白水解的负调控。蛋白酶体对 Gis1 的有限降解导致产生较小的变体，其转录活性比全长蛋白弱。较小的变体中缺失的卷曲螺旋结构域是 Gis1 中第二个转录激活结构域的一部分，对于 Gis1 的有限蛋白水解及其完全活性都是必需的。内源性 Gis1 及其变体，无论其转录能力如何，都以 Rim15 依赖的方式激活转录。然而，当由于蛋白酶体功能的过度表达或抑制导致全长 Gis1 在细胞中积累时，Gis1 的转录激活不再仅受 Rim15 控制。综上所述，这些数据强烈表明，有限降解的功能是确保 Gis1 依赖性转录受到 Rim15 激酶的严格调控。此外，我们还揭示了 Rim15 的激酶活性对于这种调控是必不可少的。
