Muller E G
Department of Biochemistry, University of Washington, Seattle 98195.
J Biol Chem. 1994 Sep 30;269(39):24466-71.
Deletion of both thioredoxin genes TRX1 and TRX2 of Saccharomyces cerevisiae reduces the rate of DNA replication. This observation, originally determined by flow cytometry, was confirmed by radiochemical labeling of synchronized cultures. Since thioredoxin is a hydrogen donor to ribonucleotide reductase, a priori the inhibition of DNA synthesis was predicted to be caused by a reduction in the deoxyribonucleotide pools. However, the levels of TTP, dCTP, dATP, and dGTP were either unchanged or slightly greater in the thioredoxin mutant (3.2, 0.91, 1.4, and 1.21 pmol/10(6) cells, respectively) versus the wild-type culture (2.5, 0.91, 1.0, and 0.68 pmol/10(6) cells, respectively). An impact on ribonucleotide reduction was seen by an increased accumulation of RNR1 and RNR2 transcripts in the thioredoxin mutant (4.3- and 6.8-fold, respectively). Increased RNR expression did not reflect a general response of the DNA replication machinery. POL1 (DNA polymerase I) and CDC8 (thymidylate kinase) transcription were unaltered, while histone H2B transcripts actually decreased by half. Two alternative models incorporating these results are discussed. One suggests that thioredoxin reduces a multiprotein complex channeling nucleotides to the replication apparatus. The second proposes that thioredoxin regulates the tempo of DNA replication directly by activating a component of the replication machinery.
酿酒酵母的硫氧还蛋白基因TRX1和TRX2的缺失会降低DNA复制速率。这一最初通过流式细胞术确定的观察结果，经同步培养物的放射化学标记得以证实。由于硫氧还蛋白是核糖核苷酸还原酶的氢供体，因此据推测，DNA合成的抑制是由脱氧核糖核苷酸池的减少所致。然而，与野生型培养物（分别为2.5、0.91、1.0和0.68 pmol/10⁶个细胞）相比，硫氧还蛋白突变体中TTP、dCTP、dATP和dGTP的水平要么未变，要么略有升高（分别为3.2、0.91、1.4和1.21 pmol/10⁶个细胞）。硫氧还蛋白突变体中RNR1和RNR2转录本的积累增加，表明对核糖核苷酸还原有影响（分别增加4.3倍和6.8倍）。RNR表达的增加并不反映DNA复制机制的普遍反应。POL1（DNA聚合酶I）和CDC8（胸苷酸激酶）的转录未改变，而组蛋白H2B转录本实际上减少了一半。文中讨论了包含这些结果的两种替代模型。一种模型认为，硫氧还蛋白可还原一种将核苷酸导向复制装置的多蛋白复合物。另一种模型则提出，硫氧还蛋白通过激活复制机制的一个组分直接调节DNA复制的节奏。
