Functional production of mammalian concentrative nucleoside transporters in Saccharomyces cerevisiae

The transport of nucleosides and nucleobases in the yeast Saccharomyces cer evisiae is reviewed and the use of this organism to study recombinant mamma lian concentrative nucleoside transport (CNT) proteins is described. A sele ction strategy based on the ability of an expressed nucleoside transporter cDNA to mediate thymidine uptake by yeast under a selective condition that depletes endogenous thymidylate was used to assess the transport capacity o f heterologous transporter proteins. The pyrimidine-nucleoside selective co ncentrative transporters from human (hCNT1) and rat (rCNT1) complemented th e imposed thymidylate depletion in S. cerevisiae, as did N-terminally trunc ated versions of hCNT1 and rCNT1 lacking up to 31 amino acids. Transporter- mediated rescue of S. cerevisiae by both nucleoside transporters was inhibi ted by cytidine, uridine and adenosine, but not by guanosine or inosine. Th is work represents the development of a new model system for the functional production of recombinant nucleoside transporters of the CNT family of mem brane proteins.