Peering down the barrel of a bacteriophage portal: the genome packaging and release valve in p22

Structure. 2011 Apr 13;19(4):496-502. doi: 10.1016/j.str.2011.02.010.


The encapsidated genome in all double-strand DNA bacteriophages is packaged to liquid crystalline density through a unique vertex in the procapsid assembly intermediate, which has a portal protein dodecamer in place of five coat protein subunits. The portal orchestrates DNA packaging and exit, through a series of varying interactions with the scaffolding, terminase, and closure proteins. Here, we report an asymmetric cryoEM reconstruction of the entire P22 virion at 7.8 Å resolution. X-ray crystal structure models of the full-length portal and of the portal lacking 123 residues at the C terminus in complex with gene product 4 (Δ123portal-gp4) obtained by Olia et al. (2011) were fitted into this reconstruction. The interpreted density map revealed that the 150 Å, coiled-coil, barrel portion of the portal entraps the last DNA to be packaged and suggests a mechanism for head-full DNA signaling and transient stabilization of the genome during addition of closure proteins.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacteriophage P22 / chemistry*
  • Bacteriophage P22 / genetics
  • Bacteriophage P22 / ultrastructure
  • Capsid Proteins / chemistry*
  • Capsid Proteins / genetics
  • Capsid Proteins / metabolism
  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • DNA, Viral / chemistry
  • DNA, Viral / genetics
  • Genome, Viral / genetics
  • Models, Molecular
  • Mutation
  • Protein Binding
  • Protein Conformation*
  • Viral Proteins / chemistry
  • Viral Proteins / metabolism
  • Virion / chemistry*
  • Virion / genetics
  • Virion / ultrastructure
  • Virus Assembly / genetics


  • Capsid Proteins
  • DNA, Viral
  • Viral Proteins
  • portal protein, bacteriophage P22