Neale G A, Mitchell A, Finch L R
J Bacteriol. 1983 Apr;154(1):17-22. doi: 10.1128/jb.154.1.17-22.1983.
By measuring the specific activity of deoxyribonucleotides isolated from DNA after the incorporation of 14C-labeled precursors with and without competition from other nucleotide precursors, we defined the major pathways of pyrimidine deoxyribonucleotide synthesis in Mycoplasma mycoides subsp. mycoides. Uracil, guanine, and thymine are required for the synthesis of nucleotides. Cytidine competed effectively with uracil to provide all of the deoxycytidine nucleotide, as well as most of the deoxyribose-1-phosphate, for the synthesis of thymidylate from thymine via thymidine phosphorylase. Each of dUMP, dCMP, and dTMP competed with cytidine for incorporation into DNA thymidylate. Appreciable incorporation of exogenous deoxyribonucleoside 5'-monophosphates into DNA without prior dephosphorylation was observed. Dephosphorylation also occurred since the added deoxyribonucleotide provided phosphate for the synthesis of the other nucleotides in DNA in competition with the 32Pi in the growth medium. Hydroxyurea inhibited cell growth and decreased the intracellular level of dATP, consistent with the action of a ribonucleoside diphosphate reductase with regulatory properties similar to those of the Escherichia coli enzyme.
通过测量在有或没有其他核苷酸前体竞争的情况下，掺入14C标记前体后从DNA中分离出的脱氧核糖核苷酸的比活性，我们确定了蕈状支原体丝状亚种嘧啶脱氧核糖核苷酸合成的主要途径。尿嘧啶、鸟嘌呤和胸腺嘧啶是核苷酸合成所必需的。胞苷能有效地与尿嘧啶竞争，通过胸苷磷酸化酶从胸腺嘧啶合成胸苷酸时，为所有的脱氧胞苷核苷酸以及大部分脱氧核糖-1-磷酸提供原料。脱氧尿苷一磷酸（dUMP）、脱氧胞苷一磷酸（dCMP）和脱氧胸苷一磷酸（dTMP）中的每一种都与胞苷竞争掺入DNA胸苷酸中。观察到外源脱氧核糖核苷5'-单磷酸在没有预先去磷酸化的情况下大量掺入DNA。去磷酸化也会发生，因为添加的脱氧核苷酸会与生长培养基中的32Pi竞争，为DNA中其他核苷酸的合成提供磷酸。羟基脲抑制细胞生长并降低细胞内dATP水平，这与具有类似于大肠杆菌酶的调节特性的核糖核苷二磷酸还原酶的作用一致。
