Formation of Complexes Between O Proteins and Replication Origin Regions of Shiga Toxin-Converting Bacteriophages

Abstract

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.

Replication Region Analysis Reveals Non-lambdoid Shiga Toxin Converting Bacteriophages

“…They have very similar replication regions including the O and P genes, which share more than 90% nucleotide sequence identity (Plunkett et al, 1999). The similarity between their replication proteins, especially the O protein, has also been confirmed by functional studies (Kozłowska et al, 2020).…”

Molecular Modeling the Proteins from the exo-xis Region of Lambda and Shigatoxigenic Bacteriophages

“…In a mouse model, the introduction of Stx + phage 933W into a non-pathogenic E. coli strain is sufficient to produce highly lethal infection [ 11 ]. A greater number of DNA replication origins may help the Stx + phage P27 fine tune the lysogenic-lytic developmental decision in response to its microenvironment [ 12 ]. In contrast to the bacterium-phage relationship, the human-phage relationship is less characterized but nevertheless, could be an important factor to consider during infection [ 13 ].…”

High diversity in the regulatory region of Shiga toxin encoding bacteriophages

“…Stx phages have traditionally been classified into the group of lambdoid phages based on similarity in behavior, genetic structure, and regulatory system. In phage lambda and lambdoid Stx phages, the assembly of the replication complex has been studied in detail [ 46 ] but there is so far no knowledge about the proteins involved in the replication process of Eru phages. Eru7 seems to be the most widespread Eru type in Europe and, together with Eru6 and Eru9, they encode proteins containing Rha or Rha/Ash domains.…”