Preston V G, Darling A J, McDougall I M
Medical Research Council Virology Unit, Institute of Virology, Glasgow, Scotland.
Virology. 1988 Dec;167(2):458-67.
The herpes simplex virus type 1 (HSV-1) temperature-sensitive (ts) mutant, ts1222, has a defect within the gene specifying the small subunit of ribonucleotide reductase. Sequence determination of the lesion revealed that the mutant DNA had a single base pair deletion at the 3' end of the gene. The mutation altered the translational reading frame such that the codons of all but one of the last 15 amino acids of the protein were changed and the termination codon removed. Although ts1222 did not induce detectable amounts of enzyme activity at both 31 degrees and 39.5 degrees, it replicated as well as wild-type virus at 31 degrees in exponentially growing tissue culture cells under one step growth conditions. At 39.5 degrees, however, ts1222 behaved as a ts mutant. These findings suggest that at low temperatures the virus-coded enzyme is dispensable for virus growth in actively dividing tissue culture cells but at high temperatures the enzyme is essential for virus replication. Under these conditions altered properties of the host cell contribute to the ts phenotype of the mutant. In the presence of hydroxyurea, which inactivates both the cellular and virus ribonucleotide reductases, growth of the mutant at 31 degrees was inhibited more than wild-type virus replication. Growth of the mutant at the permissive temperature was also sensitive to high concentrations of thymidine whereas wild-type virus multiplication was resistant to the nucleoside. It is therefore likely that ts1222 is dependent on the cellular ribonucleotide reductase for growth at this temperature. In serum-starved cells, growth of the mutant virus at 31 degrees was severely impaired. Thus, like thymidine kinase, the HSV-coded ribonucleotide reductase is required for virus multiplication in resting tissue culture cells.
单纯疱疹病毒1型（HSV - 1）温度敏感（ts）突变体ts1222在编码核糖核苷酸还原酶小亚基的基因内存在缺陷。对该损伤进行序列测定发现，突变体DNA在基因的3'端有一个单碱基对缺失。该突变改变了翻译阅读框，使得蛋白质最后15个氨基酸中除一个之外的所有密码子都发生了变化，并且终止密码子被去除。虽然ts1222在31℃和39.5℃时均未诱导出可检测到的酶活性，但在一步生长条件下，它在指数生长的组织培养细胞中于31℃时的复制情况与野生型病毒相同。然而，在39.5℃时，ts1222表现为温度敏感突变体。这些发现表明，在低温下，病毒编码的酶对于活跃分裂的组织培养细胞中的病毒生长是可有可无的，但在高温下，该酶对于病毒复制是必不可少的。在这些条件下，宿主细胞特性的改变导致了突变体的温度敏感表型。在存在羟基脲（它会使细胞和病毒的核糖核苷酸还原酶均失活）的情况下，突变体在31℃时的生长受到的抑制比野生型病毒复制更严重。突变体在允许温度下的生长也对高浓度胸苷敏感，而野生型病毒增殖对该核苷具有抗性。因此，很可能ts1222在这个温度下的生长依赖于细胞核糖核苷酸还原酶。在血清饥饿的细胞中，突变病毒在31℃时的生长严重受损。因此，与胸苷激酶一样，HSV编码的核糖核苷酸还原酶对于静止的组织培养细胞中的病毒增殖是必需的。
