GUP1 and its close homologue GUP2, encoding multimembrane-spanning proteins involved in active glycerol uptake in Saccharomyces cerevisiae

Many yeast species can utilize glycerol, both as a sole carbon source and a s an osmolyte. In Saccharomyces cerevisiae, physiological studies have prev iously shown the presence of an active uptake system driven by electrogenic proton symport. We have used transposon mutagenesis to isolate mutants aff ected in the transport of glycerol into the cell. Here we present the ident ification of YGL084c, encoding a multimembrane-spanning protein, as being e ssential for proton symport of glycerol into S. cerevisiae. The gene is nam ed GUP1 (glycerol uptake) and, for growth on glycerol, is important as a ca rbon and energy source. In addition, in strains deficient in glycerol produ ction it also provides osmotic protection by the addition of glycerol. Anot her open reading frame (ORF), YPL189w, presenting a high degree of homology to YGL084c, similarly appears to be involved in active glycerol uptake in salt-containing glucose-based media in strains deficient in glycerol produc tion. Analogously, this gene is named GUP2. To our knowledge, this is the f irst report on a gene product involved in active transport of glycerol in y easts. Mutations with the same phenotypes occurred in two other ORFs of pre viously unknown function, YDL074c and YPL180w.