Hall S T, Penny J I, Gero A M, Krishna S
School of Biochemistry and Molecular Genetics, The University of NSW, Sydney, NSW, 2052, Australia.
Exp Parasitol. 1998 Oct;90(2):181-8. doi: 10.1006/expr.1998.4320.
The expression of purine-specific nucleoside and base transporters of Crithidia luciliae has been demonstrated in Xenopus laevis oocytes. Poly(A)+-mRNA from C. luciliae, cultured in either purine-replete or purine-starved conditions, was microinjected into X. laevis oocytes. For "purine-replete" mRNA, expression of adenosine and hypoxanthine uptake in microinjected X. laevis oocytes was increased on average 9- and 3-fold above water-injected controls, respectively. Expression of adenosine and hypoxanthine uptake in oocytes microinjected with "purine-starved" mRNA was 8 and 3-fold above water-injected controls, respectively. Substrate competition indicated an adenosine/deoxyadenosine transporter and a separate base transporter specific for hypoxanthine. In contrast to C. luciliae in vivo, where the level of activity of adenosine and hypoxanthine transport was regulated by the level of purines in the medium, the heterologous expression of these transporters (from both purine replete and deplete cultures) in X. laevis oocytes was independent of the extracellular purine concentration. These results may suggest that the presence of specific transporter message is independent of the extracellular purine content, indicating that the regulation of activation and expression of these transporters in C. luciliae may not be under transcriptional control.
在非洲爪蟾卵母细胞中已证实了利什曼原虫嘌呤特异性核苷和碱基转运蛋白的表达。将在嘌呤充足或嘌呤饥饿条件下培养的利什曼原虫的聚腺苷酸加尾mRNA显微注射到非洲爪蟾卵母细胞中。对于“嘌呤充足”的mRNA，显微注射的非洲爪蟾卵母细胞中腺苷和次黄嘌呤摄取的表达分别比注射水的对照平均增加了9倍和3倍。用“嘌呤饥饿”的mRNA显微注射的卵母细胞中腺苷和次黄嘌呤摄取的表达分别比注射水的对照高8倍和3倍。底物竞争表明存在一种腺苷/脱氧腺苷转运蛋白和一种单独的对次黄嘌呤特异的碱基转运蛋白。与利什曼原虫体内情况相反，在利什曼原虫体内腺苷和次黄嘌呤转运的活性水平受培养基中嘌呤水平的调节，而这些转运蛋白（来自嘌呤充足和缺乏的培养物）在非洲爪蟾卵母细胞中的异源表达与细胞外嘌呤浓度无关。这些结果可能表明特异性转运蛋白信息的存在与细胞外嘌呤含量无关，这表明利什曼原虫中这些转运蛋白的激活和表达调控可能不受转录控制。
