Ahlgren-Berg Alexandra, Henriksson-Peltola Petri, Sehlén Wilhelmina, Haggård-Ljungquist Elisabeth
Department of Genetics, Microbiology and Toxicology, Stockholm University, S-106 91 Stockholm, Sweden.
Nucleic Acids Res. 2007;35(10):3167-80. doi: 10.1093/nar/gkm171. Epub 2007 May 7.
Bacteriophages P2 and WPhi are heteroimmune members of the P2-like family of temperate Escherichia coli phages. Temperate phages can grow lytically or form lysogeny after infection. A transcriptional switch that contains two con-vergent promoters, Pe and Pc, and two repressors regulate what life mode to enter. The immunity repressor C is the first gene of the lysogenic operon, and it blocks the early Pe promoter. In this work, some characteristics of the C proteins of P2 and WPhi are compared. An in vivo genetic analysis shows that WPhi C, like P2 C, has a strong dimerization activity in the absence of its DNA target. Both C proteins recognize two directly repeated sequences, termed half-sites and a strong bending is induced in the respective DNA target upon binding. P2 C is unable to bind to one half-site as opposed to WPhi, but both half-sites are required for repression of WPhi Pe. A reduction from three to two helical turns between the centers of the half-sites in WPhi has no significant effect on the capacity to repress Pe. However, the protein-DNA complexes formed differ, as determined by electrophoretic mobility shift experiments. A difference in spontaneous phage production is observed in isogenic lysogens.
噬菌体P2和WPhi是温和型大肠杆菌噬菌体P2样家族的异免疫成员。温和型噬菌体感染后可以进行裂解生长或形成溶原状态。一个包含两个反向启动子Pe和Pc以及两个阻遏物的转录开关调控着进入何种生活模式。免疫阻遏物C是溶原操纵子的第一个基因，它阻断早期的Pe启动子。在这项工作中，对P2和WPhi的C蛋白的一些特性进行了比较。一项体内遗传分析表明，与P2 C一样，WPhi C在没有其DNA靶点时具有很强的二聚化活性。两种C蛋白都识别两个直接重复序列，称为半位点，并且在结合时各自的DNA靶点会诱导强烈的弯曲。与WPhi不同，P2 C无法结合一个半位点，但WPhi抑制Pe需要两个半位点。WPhi中半位点中心之间的螺旋匝数从三圈减少到两圈对抑制Pe的能力没有显著影响。然而，通过电泳迁移率变动实验确定，形成的蛋白质-DNA复合物有所不同。在同基因溶原菌中观察到自发噬菌体产生的差异。
