Expression studies of GUP1 and GUP2 genes involved in glycerol active transport in Saccharomyces cerevisiae, using semi-quantitative RT-PCR

Glycerol active uptake in Saccharomyces cerevisiae, characterised physiologically as a proton symport, was previously described as repressed by glucose, induced by growth on non-fermentable carbon sources and unresponsive to growth under salt stress. GUP1 and GUP2 were identified and characterised as genes involved in glycerol active uptake. Using semi-quantitative RT-PCR, GUP1 and GUP2 transcription was measured. Unlike active transport activity determined previously, this was shown to be constitutive and not affected by either glucose repression or growth under salt stress. Furthermore, transcription of GUP1 and GUP2 was not affected in the gpd1 gpd2 mutant strain grown under salt stress in the presence of small amounts of glycerol, in which case a very high V-max of glycerol uptake was reported. Intracellular compounds were determined. Glycerol, acetate and trehalose were found to be the major compounds accumulated. Surprisingly, the gpd1 gpd2 mutant was found to produce significant amounts of glycerol. Yet, the results provide no evidence for a correlation between the amount of each compound and the glycerol transport activity in any of the strains.