Functional characterization of sucrose binding protein-mediated sucrose uptake in yeast

A sucrose binding protein was identified whose temporal and spatial patterns of mRNA expression and localization patterns of protein were tightly correlated with the active uptake of sucrose in several cell types. Heterologous expression of the sucrose binding protein in yeast strains have allowed a functional characterization of sucrose uptake as mediated by this protein. Ectopic expression of the sucrose binding protein in the susy7/ura3 yeast strain restored the ability of this strain to grow on medium containing sucrose as a sole carbon source. Further characterization of the kinetics of [(14)C]-sucrose uptake indicate that the sucrose binding protein mediates the uptake of sucrose in a non-saturable, linear manner and that this uptake is relatively insensitive to pH or treatment with protonophores. These biochemical attributes of sucrose binding protein-mediated sucrose uptake mimic the well characterized linear, non-saturable uptake of sucrose described in higher plants. The sucrose binding protein is a unique plasma membrane protein and shares sequence similarity to the seed storage proteins. The sucrose binding protein may mediate sucrose uptake across the plasma membrane in a plant-specific manner.