UPS1 and UPS2 from Arabidopsis mediate high affinity transport of uracil and 5-fluorouracil
UPS1 and UPS2 from Arabidopsis mediate high affinity transport of uracil and 5-fluorouracil
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DOI：
10.1074/jbc.m405433200
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发表时间：
2004-10-22
影响因子：
4.8
通讯作者：
Desimone, M
中科院分区：
文献类型：
--
作者：
Schmidt, A;Su, YH;Desimone, M
补救途径在向细胞提供核碱基方面发挥重要作用，细胞无法合成足够的量以满足其需要。嘧啶的细胞摄取系统已被描述，但在高等真核生物中，胸腺嘧啶和尿嘧啶的转运蛋白尚未确定。最近在拟南芥和菜豆中分别发现了两种植物转运蛋白AtUPS 1和PvUPS 1。然而，与热带豆科植物相反，拟南芥主要使用氨基酸进行长距离运输。尿囊素的转运在被子植物中尚未被描述。因此，拟南芥酰脲通透酶（UPS）转运蛋白的生理底物可能是与尿囊素结构相关的化合物。AtUPS家族的两个成员的底物特异性的详细分析表明，AtUPS 1和AtUPS 2介导高亲和力尿嘧啶和5-氟尿嘧啶（一种有毒的尿嘧啶类似物）运输时，在酵母和非洲爪蟾卵母细胞中表达。与萌发和早期幼苗发育过程中的功能一致，AtUPS 1表达在幼苗发育的早期阶段瞬时诱导，随后上调AtUPS 2表达。拟南芥ups 2插入突变体和ups 1株系，其中转录水平降低的转录后基因沉默，更耐受5-氟尿嘧啶相比，野生型植物。结果表明，在拟南芥中UPS转运蛋白是尿嘧啶和潜在的其他核碱基的主要转运蛋白，而在进化过程中，豆类可能利用了UPS蛋白的低选择性进行尿囊素的长距离运输。
Salvage pathways play an important role in providing nucleobases to cells, which are unable to synthesize sufficient amounts for their needs. Cellular uptake systems for pyrimidines have been described, but in higher eukaryotes, transporters for thymine and uracil have not been identified. Two plant transporters, AtUPS1 and PvUPS1, were recently identified as transporters for allantoin in Arabidopsis and French bean, respectively. However, Arabidopsis, in contrast to tropical legumes, uses mainly amino acids for long distance transport. Allantoin transport has not been described in the Brassicaceae. Thus, the physiological substrates of ureide permease (UPS) transporters in Arabidopsis may be compounds structurally related to allantoin. A detailed analysis of the substrate specificities of two members of the AtUPS family shows that AtUPS1 and AtUPS2 mediate high affinity uracil and 5-fluorouracil (a toxic uracil analogue) transport when expressed in yeast and Xenopus oocytes. Consistent with a function during germination and early seedling development, AtUPS1 expression is transiently induced during the early stages of seedling development followed by up-regulation of AtUPS2 expression. Arabidopsis ups2 insertion mutants and ups1 lines, in which transcript levels were reduced by post-transcriptional gene silencing, are more tolerant to 5-fluorouracil as compared with wild type plants. The results suggest that in Arabidopsis UPS transporters are the main transporters for uracil and potentially other nucleobases, whereas during evolution legumes may have taken advantage of the low selectivity of UPS proteins for long distance transport of allantoin.