Protein Targeting Regulating Snf1 Localization

Snf1, a serine-threonine kinase in Saccharomyces cerevisiae, is activated under conditions of glucose deprivation and regulates the expression of specific genes involved in cellular metabolism. Snf1 can control the activity of specific transcriptional activators and repressors and of RNA polymerase II in the nucleus. Snf1 protein kinases exist as heterotrimers with a subunit and one of three different β subunits--Gal83, Sip1, or Sip2--but the significance of each interaction is unclear. Vincent et al. showed that under glucose-depleted conditions, expressed chimeric proteins consisting of green fluorescent protein (GFP) fused to Sip1 or Sip2 localized to the vacuole or cytoplasm, respectively, whereas GFP-Gal83 localized to the nucleus, suggesting that Gal83 targets Snf1 to the nucleus. GFP-Snf1 also localized to the nucleus in glucose-depleted conditions. Translocation of Snf1-Gal83 to the nucleus was independent of the kinase activity of Snf1. In the presence of glucose, Snf1-Gal83 was excluded from the nucleus in a manner dependent on glucose phosphorylation. The authors note that independent regulation of the activity and localization of Snf1 should enhance the versatility of physiological regulation mediated by this protein kinase.

O. Vincent, R. Townley, S. Kuchin, M. Carlson, Subcellular localization of the Snf1 kinase is regulated by specific β subunits and a novel glucose signaling mechanism. Genes Dev. 15, 1104-1114 (2001). [Abstract] [Full Text]