F-box proteins represent the substrate-specificity determinants of the SCF ubiquitin ligase complex. We previously reported that the F-box protein Grr1p is one of the proteins involved in the transmission of glucose-generated signal for proteolysis of the galactose transporter Gal2p and fructose-1,6-bisphosphatase. In this study, we show that the other components of SCF(Grr1), including Skp1, Rbx1p, and the ubiquitin-conjugating enzyme Cdc34, are also necessary for glucose-induced Gal2p degradation. This suggests that transmission of the glucose signal involves an SCF(Grr1)-mediated ubiquitination step. However, almost superimposable ubiquitination patterns of Gal2p observed in wild-type and grr1Delta mutant cells imply that Gal2p is not the primary target of SCF(Grr1) ubiquitin ligase. In addition, we demonstrate here that glucose-induced Gal2p proteolysis is a cell-cycle-independent event.

Institute of Physiology Department of Membrane Transport Academy of Science of the Czech Republic 142 20 Prague Czech Republic

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