Abstract #98B

Two vacuolar yeast sugar permeases are involved in response to heat shock and osmotic stress. Carsten Fruehbeis, Eckhard Boles. Institute of Molecular Biosciences, University of Frankfurt, Frankfurt, Germany.
   So far, nothing is known about vacuolar sugar permeases in the yeast Saccharomyces cerevisiae. We found two uncharacterized members of the sugar permease family located to the vacuolar membrane. The vacuolar localization was not changed in mutants defective for endocytosis, ensuring the vacuolar localization is not due to degradation. Therefore we suggest that these proteins could be vacuolar sugar permeases. To analyze how these proteins are transported to the vacuole further localization studies were performed, indicating both proteins take a similar route to the vacuole as the vacuolar ATPase subunit Vph1. The deletion of both genes leads to a decreased ability of the mutants to survive heat shock. Additionally, a genome wide screen for genetic interactions with these two uncharacterized genes revealed an interaction with the plasma membrane glycerol transporter Fps1, which controls the accumulation and release of the compatible solute glycerol in osmoregulation. The additional deletion of the two permeases in a fps1-knockout strain increases the sensitivity to hypo-osmotic shock. As the ability to survive stress conditions like osmotic stress and heat shock could correlate with the cellular level of the dissaccharide trehalose and trehalose seems to be a putative substrate for the intracellular permeases, we assume the vacuolar sugar permeases could play a role in trehalose metabolism. But also an involvement in glycerol metabolism is indicated by the genetic interaction with Fps1 and the fact that the glycerol transporter Stl1 is also a member of the sugar transporter family.

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