In a complex and ever-changing environment, various signal transduction pathways mediate outside signals and stress to a living cell and its intracellular responses. Eukaryotic cells utilize the DNA synthesis phase (S-phase) checkpoint to respond to DNA damage and replication stress, and the activation of the S-phase checkpoint defers the routine progression in the S phase. Through the analysis of microfluidic single-cell measurements, we find that the behavior of yeast cells exhibits bimodal distribution in the activation of the S-phase checkpoint, and the nonactivated portion of cells obeys the exponential decay law over time, the rate of which is dictated by HU dosage. Mathematical modeling and further experimental evidence from different mutant strains support the idea that the activation of the yeast S-phase checkpoint is a stochastic barrier-crossing process in a double-well system, where the barrier height is determined by both DNA replication stress and autophosphorylation of the key effector kinase Rad53. Our approach, as a novel methodology, is generally applicable to quantitative analysis of the signal transduction pathways at the single-cell level.

中文翻译：

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随机性触发萌芽酵母中S相检查点途径的激活

在复杂且不断变化的环境中，各种信号转导途径介导外部信号，并向活细胞及其细胞内反应施加压力。真核细胞利用DNA合成阶段（S阶段）检查点来应对DNA损伤和复制压力，而S阶段检查点的激活阻止了S阶段的常规进程。通过对微流体单细胞测量的分析，我们发现酵母细胞的行为在S期检查点的激活中表现出双峰分布，并且未激活的细胞随时间服从指数衰减定律，其速率为由HU剂量决定。来自不同突变菌株的数学模型和进一步的实验证据支持以下观点：酵母双相系统检查点的激活是双孔系统中的随机壁垒穿越过程，其中壁垒高度由DNA复制应力和自磷酸化决定关键效应激酶Rad53的表达。我们的方法，作为一种新颖的方法，通常适用于在单细胞水平上定量分析信号转导途径。