Role of Snf1p in regulation of intracellular sorting of the lactose and galactose transporter Lac12p in Kluyveromyces lactis.

The protein kinase Snf1/AMPK plays a central role in carbon and energy homeostasis in yeasts and higher eukaryotes. To work out which aspects of the Snf1-controlled regulatory network are conserved in evolution, the Snf1 requirement in galactose metabolism was analyzed in the yeast Kluyveromyces lactis. Whereas galactose induction was only delayed, K. lactis snf1 mutants failed to accumulate the lactose/galactose H+ symporter Lac12p in the plasma membran,e as indicated by Lac12-green fluorescent protein fusions. In contrast to wild-type cells, the fusion protein was mostly intracellular in the mutant. Growth on galactose and galactose uptake could be restored by the KHT3 gene, which encodes a new transporter of the HXT subfamily of major facilitators These findings indicate a new role of Snf1p in regulation of sugar transport in K. lactis.