Department of Molecular Biology and Functional Genomics, Arrhenius Laboratories for Natural Sciences, Stockholm University, SE-10691 Stockholm, Sweden.
Department of Molecular Biology, Swedish University of Agricultural Sciences, Uppsala Biomedical Center, SE-75124 Uppsala, Sweden.
J Biol Chem. 2013 Mar 22;288(12):8198-8208. doi: 10.1074/jbc.M112.442434. Epub 2013 Jan 31.
Ribonucleotide reductases (RNRs) catalyze the only pathway for de novo synthesis of deoxyribonucleotides needed for DNA replication and repair. The vast majority of eukaryotes encodes only a class I RNR, but interestingly some eukaryotes, including the social amoeba Dictyostelium discoideum, encode both a class I and a class II RNR. The amino acid sequence of the D. discoideum class I RNR is similar to other eukaryotic RNRs, whereas that of its class II RNR is most similar to the monomeric class II RNRs found in Lactobacillus spp. and a few other bacteria. Here we report the first study of RNRs in a eukaryotic organism that encodes class I and class II RNRs. Both classes of RNR genes were expressed in D. discoideum cells, although the class I transcripts were more abundant and strongly enriched during mid-development compared with the class II transcript. The quaternary structure, allosteric regulation, and properties of the diiron-oxo/radical cofactor of D. discoideum class I RNR are similar to those of the mammalian RNRs. Inhibition of D. discoideum class I RNR by hydroxyurea resulted in a 90% reduction in spore formation and decreased the germination viability of the surviving spores by 75%. Class II RNR could not compensate for class I inhibition during development, and an excess of vitamin B12 coenzyme, which is essential for class II activity, did not improve spore formation. We suggest that class I is the principal RNR during D. discoideum development and growth and is important for spore formation, possibly by providing dNTPs for mitochondrial replication.
核糖核苷酸还原酶（RNRs）催化脱氧核苷酸从头合成的唯一途径，这些脱氧核苷酸是 DNA 复制和修复所必需的。绝大多数真核生物只编码一种 I 类 RNR，但有趣的是，一些真核生物，包括黏菌 Dictyostelium discoideum，既编码一种 I 类 RNR，也编码一种 II 类 RNR。D. discoideum I 类 RNR 的氨基酸序列与其他真核 RNR 相似，而其 II 类 RNR 的氨基酸序列与乳杆菌属和少数其他细菌中的单体 II 类 RNR 最相似。在这里，我们报告了首例在编码 I 类和 II 类 RNR 的真核生物中研究 RNR 的研究。两种 RNR 基因都在 D. discoideum 细胞中表达，尽管 I 类转录本在中期发育过程中更为丰富，并且比 II 类转录本强烈富集。D. discoideum I 类 RNR 的四级结构、别构调节和双铁-氧/自由基辅因子的性质与哺乳动物 RNRs 相似。羟基脲对 D. discoideum I 类 RNR 的抑制导致孢子形成减少 90%，并使存活孢子的萌发活力降低 75%。在发育过程中，II 类 RNR 不能补偿 I 类抑制，并且过量的维生素 B12 辅酶，这是 II 类活性所必需的，不能改善孢子形成。我们认为，I 类是 D. discoideum 发育和生长过程中的主要 RNR，对孢子形成很重要，可能是通过为线粒体复制提供 dNTP。
