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Bacteriophages, also known as phages, are specialized viruses that infect bacteria. A key characteristic of phages is their distinctive “head-tail” morphology. A phage begins the infection process (i.e., lytic cycle) by attaching to the outside of a bacterial cell. Attachment is accomplished via proteins in the phage tail that bind to specific receptor proteins on the outer surface of the bacterium. The tail injects the phage’s DNA genome into the bacterial cytoplasm. In the...
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Bacteriophages, or phages, are viruses that specifically infect bacteria. Among them, T-even bacteriophages, such as T4, exhibit a well-characterized lytic replication cycle in Escherichia coli (E. coli). This process ensures the rapid proliferation of the virus while ultimately leading to the destruction of the bacterial host.Attachment and DNA InjectionThe infection process begins with the recognition and binding of the T4 phage to the E. coli cell surface. Tail fibers of the phage...
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The lysogenic cycle is a crucial viral replication strategy that allows bacteriophages to persist within host cells without immediately destroying them. This process is primarily observed in temperate phages, such as bacteriophage lambda (λ), which infects Escherichia coli. The cycle allows the viral genome to persist across bacterial generations while keeping host cells viable.Integration of the Viral GenomeUpon infection, bacteriophage lambda attaches to the bacterial surface and injects...
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Bacteriophage SPP1 pac Cleavage: A Precise Cut without Sequence Specificity Requirement.

Karima Djacem1, Paulo Tavares1, Leonor Oliveira1

  • 1Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Univ Paris-Sud, Université Paris-Saclay, 91198 Gif-sur-Yvette, France.

Journal of Molecular Biology
|January 14, 2017
PubMed
Summary

Bacteriophage DNA packaging terminase subunits (TerS and TerL) precisely cleave DNA at the pac site. Minimal sequences in pacR and pacL, including a poly-A tract, are sufficient to orient TerL for accurate cleavage, independent of the targeted DNA sequence.

Keywords:
DNA packagingbacteriophagegenome recognitionpac cleavageterminase

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Area of Science:

  • Molecular Biology
  • Virology
  • Genetics

Background:

  • DNA packaging in tailed bacteriophages is crucial for viral replication.
  • Terminase subunits (TerS and TerL) recognize and cleave the pac site to initiate packaging.
  • Previous studies identified TerS binding sites (pacR, pacL) and TerL cleavage site (pacC) in SPP1 phage.

Purpose of the Study:

  • To identify the minimal pac-specific DNA sequences required for terminase-mediated cleavage.
  • To understand the mechanism of precise DNA cleavage by terminase subunits at the pac site.
  • To investigate the conservation of pac cleavage site and sequence requirements across related phages.

Main Methods:

  • Sequence degeneration and deletion analyses of pacR, pacL, and pacC regions.
  • Functional assays to assess pac cleavage by terminase subunits.
  • Comparative studies with SPP1-related bacteriophages.

Main Results:

  • A 5-bp polyadenine tract in pacR and part of the pacL sequence are critical for orienting terminase.
  • Extensive sequence variations in pacR and pacC do not alter the precise cleavage position.
  • The cleavage site (pacC) is accurately targeted even with degenerated sequences, indicating sequence-independent positioning.

Conclusions:

  • Minimal DNA sequences, specifically a poly-A tract in pacR and part of pacL, are sufficient for accurate terminase-mediated DNA cleavage.
  • The precise positioning of the TerL nuclease at pacC is achieved through specific TerS interactions and is largely independent of the targeted DNA sequence.
  • This mechanism ensures conserved cleavage site accuracy across related bacteriophages despite sequence variations.