Schnorr K M, Nygaard P, Laloue M
Laboratoire de Biologie Cellulaire, INRA, Centre de Recherches de Versailles, France.
Plant J. 1994 Jul;6(1):113-21. doi: 10.1046/j.1365-313x.1994.6010113.x.
Glycinamide ribonucleotide (GAR) synthetase, GAR transformylase and aminoimidazole ribonucleotide (AIR) synthetase are the second, third and fifth enzymes in the 10-step de novo purine biosynthetic pathway. From a cDNA library of Arabidopsis thaliana, cDNAs encoding the above three enzymes were cloned by functional complementation of corresponding Escherichia coli mutants. Each of the cDNAs encode peptides comprising the complete enzymatic domain of either GAR synthetase, GAR transformylase or AIR synthetase. Comparisons of the three Arabidopsis purine biosynthetic enzymes with corresponding enzymes/polypeptide-fragments from procaryotic and eucaryotic sources indicate a high degree of conserved homology at the amino acid level, in particular with procaryotic enzymes. Assays from extracts of E. coli expressing the complementing clones verified the specific enzymatic activity of Arabidopsis GAR synthetase and GAR transformylase. Sequence analysis, as well as Northern blot analysis indicate that Arabidopsis has single and monofunctional enzymes. In this respect the organization of these three plant purine biosynthesis genes is fundamentally different from the multifunctional purine biosynthesis enzymes characteristic of other eucaryotes and instead resembles the one gene, one enzyme relationship found in procaryotes.
甘氨酰胺核糖核苷酸（GAR）合成酶、GAR转甲酰基酶和氨基咪唑核糖核苷酸（AIR）合成酶是从头合成嘌呤的10步生物合成途径中的第二、第三和第五种酶。从拟南芥的cDNA文库中，通过相应大肠杆菌突变体的功能互补克隆出了编码上述三种酶的cDNA。每个cDNA编码的肽包含GAR合成酶、GAR转甲酰基酶或AIR合成酶的完整酶结构域。将三种拟南芥嘌呤生物合成酶与来自原核生物和真核生物来源的相应酶/多肽片段进行比较，结果表明在氨基酸水平上具有高度保守的同源性，特别是与原核生物的酶。对表达互补克隆的大肠杆菌提取物进行的分析验证了拟南芥GAR合成酶和GAR转甲酰基酶的特定酶活性。序列分析以及Northern印迹分析表明拟南芥具有单一的单功能酶。在这方面，这三个植物嘌呤生物合成基因的组织与其他真核生物特有的多功能嘌呤生物合成酶有根本不同，反而类似于原核生物中发现的一个基因一种酶的关系。
