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 H+/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 SQ-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 still not affected in the gpd1gpd2 mutant strain grown under salt stress in the presence of small amounts of glycerol, in which case a very high Vmax of glycerol uptake has been reported. Intracellular compounds were determined. Glycerol, acetate and trehalose were found to be the major compounds accumulated. Surprisingly, gpd1gpd2 mutant was shown to produce significant amounts of glycerol. Yet, results do not evidence a correlation between the amount of each compound and glycerol transport activity in any of the strains