Center for Models of Life, Niels Bohr Institute, University of Copenhagen, Denmark.
Biophys J. 2011 Jan 19;100(2):313-21. doi: 10.1016/j.bpj.2010.12.3681.
After infection of a sensitive host temperate phages may enter either a lytic or a lysogenic pathway leading to new phage assembly or silencing as a prophage, respectively. The decision about which pathway to enter is centered in the genetic switch of the phage. In this work, we explore the bistable genetic switch of bacteriophage TP901-1 through experiments and statistical mechanical modeling. We examine the activity of the lysogenic promoter P(R) at different concentrations of the phage repressor, CI, and compare the effect of CI on P(R) in the presence or absence of the phage-encoded MOR protein expressed from the lytic promoter P(L). We find that the presence of large amounts of MOR prevents repression of the P(R) promoter, verifying that MOR works as an antirepressor. We compare our experimental data with simulations based on previous mathematical formulations of this switch. Good agreement between data and simulations verify the model of CI repression of P(R). By including MOR in the simulations, we are able to discard a model that assumes that CI and MOR do not interact before binding together at the DNA to repress P(R). The second model of Pr repression assumes the formation of a CI:MOR complex in the cytoplasm. We suggest that a CI:MOR complex may exist in different forms that either prevent or invoke P(R) repression, introducing a new twist on mixed feedback systems.
在感染敏感宿主后，温和噬菌体可能进入裂解途径或溶源途径，分别导致新噬菌体的组装或沉默作为原噬菌体。进入哪种途径的决定取决于噬菌体的遗传开关。在这项工作中，我们通过实验和统计力学建模来探索噬菌体 TP901-1 的双稳态遗传开关。我们研究了溶源启动子 P(R) 在不同噬菌体阻遏物 CI 浓度下的活性，并比较了在存在或不存在从裂解启动子 P(L)表达的噬菌体编码 MOR 蛋白的情况下，CI 对 P(R)的影响。我们发现大量 MOR 的存在阻止了 P(R)启动子的抑制，验证了 MOR 作为反阻遏物的作用。我们将实验数据与基于该开关的先前数学公式的模拟进行比较。数据与模拟之间的良好一致性验证了 CI 对 P(R)的抑制模型。通过在模拟中包含 MOR，我们能够排除一种假设，即 CI 和 MOR 在结合到 DNA 上抑制 P(R)之前不会相互作用。第二种 Pr 抑制模型假设 CI:MOR 复合物在细胞质中形成。我们认为，CI:MOR 复合物可能以不同的形式存在，这些形式可以防止或引发 P(R)的抑制，为混合反馈系统引入了一个新的变化。
