Ubiquitination is a versatile tool used by all eukaryotic organisms for controlling the stability, function, and intracellular localization of a multitude of proteins. I will attempt to bring together our recent data on the down-regulation of twoyeast model proteins, the galactose transporter Gal2 and fructose-1,6-bisphosphatase, by ubiquitin-dependent proteolysis triggered by the additionof easily fermentable carbon sources.