Structural characterization of the bacteriophage T7 tail machinery

J Biol Chem. 2013 Sep 6;288(36):26290-26299. doi: 10.1074/jbc.M113.491209. Epub 2013 Jul 24.


Most bacterial viruses need a specialized machinery, called "tail," to inject their genomes inside the bacterial cytoplasm without disrupting the cellular integrity. Bacteriophage T7 is a well characterized member of the Podoviridae family infecting Escherichia coli, and it has a short noncontractile tail that assembles sequentially on the viral head after DNA packaging. The T7 tail is a complex of around 2.7 MDa composed of at least four proteins as follows: the connector (gene product 8, gp8), the tail tubular proteins gp11 and gp12, and the fibers (gp17). Using cryo-electron microscopy and single particle image reconstruction techniques, we have determined the precise topology of the tail proteins by comparing the structure of the T7 tail extracted from viruses and a complex formed by recombinant gp8, gp11, and gp12 proteins. Furthermore, the order of assembly of the structural components within the complex was deduced from interaction assays with cloned and purified tail proteins. The existence of common folds among similar tail proteins allowed us to obtain pseudo-atomic threaded models of gp8 (connector) and gp11 (gatekeeper) proteins, which were docked into the corresponding cryo-EM volumes of the tail complex. This pseudo-atomic model of the connector-gatekeeper interaction revealed the existence of a common molecular architecture among viruses belonging to the three tailed bacteriophage families, strongly suggesting that a common molecular mechanism has been favored during evolution to coordinate the transition between DNA packaging and tail assembly.

Keywords: Bacteriophage; DNA Viruses; Electron Microscopy (EM); Protein Structure; Virus Assembly; Virus Structure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriophage T7 / genetics
  • Bacteriophage T7 / metabolism
  • Bacteriophage T7 / ultrastructure*
  • Cryoelectron Microscopy
  • DNA, Viral / chemistry
  • DNA, Viral / genetics
  • DNA, Viral / metabolism
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Escherichia coli / virology
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / genetics
  • Multiprotein Complexes / metabolism
  • Multiprotein Complexes / ultrastructure*
  • Viral Proteins / chemistry
  • Viral Proteins / genetics
  • Viral Proteins / metabolism


  • DNA, Viral
  • Multiprotein Complexes
  • Viral Proteins
  • bacteriophage T7 leg protein gp17

Associated data

  • PDB/3J4A
  • PDB/3J4B