Shiga toxin-converting bacteriophages (or Stx phages) are responsible for virulence of enterohemorrhagic Escherichia coli strains. Although they belong to the group of lambdoid phages, which have served as models in studies on DNA replication mechanisms, details of regulation of replication of Stx phage genomes are poorly understood. Despite high similarity of their replication regions to that of phage lambda, considerable differences occur between them. Here, we present a comparison of origins of replication and O proteins of lambda and selected Stx phages (phages P27 and 933W). Stx initiator proteins, similarly to the lambda O protein, exist in the form of dimers. Only 4 iteron sequences are strongly bound in vitro by the O proteins, despite the presence of 6 such fragments in the Stx ori, while the function of the other two iterons is still crucial for transformation of E. coli wild-type strain by the P27-derived lambdoid plasmid. As these sequences are found in the gene coding for Stx O proteins, the sequences of these proteins themselves are also extended compared to lambda phage. Therefore, proteins O of Stx phages P27 and 933W have 13 additional amino acids. They can act as a space barrier, thus affecting the lesser packing of the O-some Stx complex compared to the structure found in lambda. Such structure of the DNA replication initiation complex may determine its lesser dependence on the processes occurring in the host cell, including transcriptional activation of the origin. Differences between molecular processes occurring during formation of replication complexes in lambda and Stx phages may indicate the specialization of the latter phages and their adaptation to specific environmental conditions where quick genetic switches are crucial.

志贺毒素转化噬菌体（或Stx噬菌体）负责肠出血性 大肠杆菌株。尽管它们属于lambdoid噬菌体的组，它们已作为DNA复制机制研究的模型，但对Stx噬菌体基因组复制调控的细节知之甚少。尽管它们的复制区与噬菌体λ的复制区高度相似，但是它们之间仍存在相当大的差异。在这里，我们介绍了λ和选定的Stx噬菌体（噬菌体P27和933W）的复制起点和O蛋白的比较。与λO蛋白相似，Stx引发剂蛋白以二聚体形式存在。仅绑定4个iteron序列体外 尽管在Stx中存在6个这样的片段 ORI，而其他两个迭代器的功能对于 大肠杆菌P27来源的lambdoid质粒产生野生型菌株。由于在编码Stx O蛋白的基因中发现了这些序列，因此与λ噬菌体相比，这些蛋白本身的序列也得到了扩展。因此，Stx噬菌体P27和933W的蛋白质O具有另外13个氨基酸。它们可以充当空间屏障，因此与lambda中发现的结构相比，对O-some Stx复合物的堆积影响较小。DNA复制起始复合物的这种结构可以确定其对宿主细胞中发生的过程的依赖性较小，包括起源的转录激活。