Department of Cell and Organism Biology, Lund University, Lund, Sweden.
FEBS J. 2012 Oct;279(20):3889-97. doi: 10.1111/j.1742-4658.2012.08747.x. Epub 2012 Sep 11.
Deoxyribonucleotides are the building blocks of DNA and can be synthesized via de novo and salvage pathways. Deoxyribonucleoside kinases (EC 2.7.1.145) salvage deoxyribonucleosides by transfer of a phosphate group to the 5' of a deoxyribonucleoside. This salvage pathway is well characterized in mammals, but in contrast, little is known about how plants salvage deoxyribonucleosides. We show that during salvage, deoxyribonucleosides can be phosphorylated by extracts of Arabidopsis thaliana into corresponding monophosphate compounds with an unexpected preference for purines over pyrimidines. Deoxyribonucleoside kinase activities were present in all tissues during all growth stages. In the A. thaliana genome, we identified two types of genes that could encode enzymes which are involved in the salvage of deoxyribonucleosides. Thymidine kinase activity was encoded by two thymidine kinase 1 (EC 2.7.1.21)-like genes (AtTK1a and AtTK1b). Deoxyadenosine, deoxyguanosine and deoxycytidine kinase activities were encoded by a single AtdNK gene. T-DNA insertion lines of AtTK1a and AtTK1b mutant genes had normal growth, although AtTK1a AtTK1b double mutants died at an early stage, which indicates that AtTK1a and AtTK1b catalyze redundant reactions. The results obtained in the present study suggest a crucial role for the salvage of thymidine during early plant development.
脱氧核苷酸是 DNA 的组成部分，可以通过从头合成和补救途径合成。脱氧核苷激酶（EC 2.7.1.145）通过将磷酸基团转移到脱氧核苷的 5'位置来补救脱氧核苷。这种补救途径在哺乳动物中得到了很好的描述，但相比之下，人们对植物如何补救脱氧核苷知之甚少。我们表明，在补救过程中，脱氧核苷可以被拟南芥提取物磷酸化为相应的单磷酸盐化合物，对嘌呤的偏好超过嘧啶。在所有生长阶段，所有组织中都存在脱氧核苷激酶活性。在拟南芥基因组中，我们鉴定了两种类型的基因，它们可能编码参与脱氧核苷补救的酶。胸苷激酶活性由两个胸苷激酶 1（EC 2.7.1.21）样基因（AtTK1a 和 AtTK1b）编码。脱氧腺苷、脱氧鸟苷和脱氧胞苷激酶活性由单个 AtdNK 基因编码。AtTK1a 和 AtTK1b 突变基因的 T-DNA 插入系具有正常的生长，尽管 AtTK1a AtTK1b 双突变体在早期死亡，这表明 AtTK1a 和 AtTK1b 催化冗余反应。本研究获得的结果表明，在植物早期发育过程中，胸苷的补救对于细胞生长和分裂是至关重要的。
