FUNCTIONAL-CHARACTERIZATION OF SUCROSE BINDING PROTEIN-MEDIATED SUCROSE UPTAKE IN YEAST

A sucrose binding protein was identified whose temporal and spatial pa tterns of mRNA expression and localization patterns of protein were ti ghtly correlated with the active uptake of sucrose in several cell typ es. Heterologous expression of the sucrose binding protein in yeast st rains have allowed a functional characterization of sucrose uptake as mediated by this protein. Ectopic expression of the sucrose binding pr otein in the susy7/ura3 yeast strain restored the ability of this stra in to grow on medium containing sucrose as a sole carbon source. Furth er characterization of the kinetics of [C-14]-sucrose uptake indicate that the sucrose binding protein mediates the uptake of sucrose in a n on-saturable, linear manner and that this uptake is relatively insensi tive to pH or treatment with protonophores. These biochemical attribut es of sucrose binding protein-mediated sucrose uptake mimic the well c haracterized linear, non-saturable uptake of sucrose described in high er plants. The sucrose binding protein is a unique plasma membrane pro tein and shares sequence similarity to the seed storage proteins. The sucrose binding protein may mediate sucrose uptake across the plasma m embrane in a plant-specific manner.