Lesage P, Yang X, Carlson M
Department of Genetics and Development, Institute of Cancer Research, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
Mol Cell Biol. 1996 May;16(5):1921-8. doi: 10.1128/MCB.16.5.1921.
The SNF1 protein kinase has been widely conserved in plants and mammals. In Saccharomyces cerevisiae, SNF1 is essential for expression of glucose-repressed genes in response to glucose deprivation. Previous studies supported a role for SNF1 in relieving transcriptional repression. Here, we report evidence that SNF1 modulates function of a transcriptional activator, SIP4, which was identified in a two-hybrid screen for interaction with SNF1. The N terminus of the predicted 96-kDa SIP4 protein is homologous to the DNA-binding domain of the GAL4 family of transcriptional activators, with a C6 zinc cluster adjacent to a coiled-coil motif The C terminus contains a leucine zipper motif and an acidic region. When bound to DNA, a LexA-SIP4 fusion activates transcription of a reporter gene. Transcriptional activation by SIP4 is regulated by glucose and depends on the SNF1 protein kinase. Moreover, SIP4 is differentially phosphorylated in response to glucose availability, and phosphorylation requires SNF1. These findings suggest that the SNF1 kinase interacts with a transcriptional activator to modulate its activity and provide the first direct evidence for a role of SNF1 in activating transcription in response to glucose limitation.
SNF1蛋白激酶在植物和哺乳动物中广泛存在。在酿酒酵母中，SNF1对于响应葡萄糖剥夺时葡萄糖抑制基因的表达至关重要。先前的研究支持SNF1在解除转录抑制中发挥作用。在此，我们报告证据表明SNF1调节转录激活因子SIP4的功能，SIP4是在与SNF1相互作用的双杂交筛选中鉴定出来的。预测的96 kDa SIP4蛋白的N末端与转录激活因子GAL4家族的DNA结合结构域同源，在卷曲螺旋基序附近有一个C6锌簇。C末端包含一个亮氨酸拉链基序和一个酸性区域。当与DNA结合时，LexA-SIP4融合蛋白激活报告基因的转录。SIP4的转录激活受葡萄糖调节，并依赖于SNF1蛋白激酶。此外，SIP4响应葡萄糖可用性而发生差异磷酸化，且磷酸化需要SNF1。这些发现表明SNF1激酶与转录激活因子相互作用以调节其活性，并为SNF1在响应葡萄糖限制时激活转录中的作用提供了首个直接证据。
