SUT1 is a putative Zn[II]2Cys6-transcription factor whose upregulation enhances both sterol uptake and synthesis in aerobically growing Saccharomyces cerevisiae cells

Budding yeast Saccharomyces cerevisiae is a facultative anaerobe whose growth upon oxygen starvation depends on its capacity to import exogenously supplied sterols, whereas the cells are not permeable to these molecules when grown aerobically. Few genes have been identified as being involved in sterol uptake. A higher SUT1 gene dosage leads to a modest, but significant, increase in sterol uptake under aerobic conditions. Based on sequence and physiological data, SUT1 is a hypoxic gene negatively regulated when the cells are grown in the presence of oxygen. We replaced the SUT1 promoter with the constitutive PMA1 gene promoter in order to enhance its transcription. We observed that sterol uptake was then comparable with that obtained with a sterol importing hem1 mutant, although the heme status of the strain was not modified in a process which still occurs when the cells are not growing. Unexpectedly, SUT1 constitutive expression led to a parallel significant increase in endogenous sterol biosynthesis. Moreover, here we present new data showing that the structurally related YPR009 gene (SUT2) is a functional homologue of SUT1, and that both gene products may represent two novel yeast regulatory proteins involved in sterol uptake.