CRITHIDIA LUCILIAE - FUNCTIONAL EXPRESSION OF NUCLEOSIDE AND NUCLEOBASE TRANSPORTERS IN XENOPUS-LAEVIS OOCYTES

The expression of purine-specific nucleoside and base transporters of Crithidia luciliae has been demonstrated in Xenopus laevis oocytes. Po ly(A)(+)-mRNA from C. luciliae, cultured in either purine-replete or p urine-starved conditions, was microinjected into X. laevis oocytes. Fo r ''purine-replete'' mRNA, expression of adenosine and hypoxanthine up take in microinjected X. laevis oocytes was increased on average 9- an d 3-fold above water-injected controls, respectively. Expression of ad enosine and hypoxanthine uptake in oocytes microinjected with ''purine -starved'' mRNA was 8 and 3-fold above water-injected controls, respec tively. Substrate competition indicated an adenosine/deoxy-adenosine t ransporter and a separate base transporter specific for hypoxanthine. In contrast to C. luciliae in vivo, where the level of activity of ade nosine and hypoxanthine transport was regulated by the level of purine s in the medium, the heterologous expression of these transporters (fr om both purine replete and deplete cultures) in X. laevis oocytes was independent of the extracellular purine concentration. These results m ay suggest that the presence of specific transporter message is indepe ndent of the extracellular purine content, indicating that the regulat ion of activation and expression of these transporters in C. luciliae may not be under transcriptional control. (C) 1998 Academic Press.