Icosahedral bacteriophage ΦX174 forms a tail for DNA transport during infection

Nature. 2014 Jan 16;505(7483):432-5. doi: 10.1038/nature12816. Epub 2013 Dec 15.


Prokaryotic viruses have evolved various mechanisms to transport their genomes across bacterial cell walls. Many bacteriophages use a tail to perform this function, whereas tail-less phages rely on host organelles. However, the tail-less, icosahedral, single-stranded DNA ΦX174-like coliphages do not fall into these well-defined infection processes. For these phages, DNA delivery requires a DNA pilot protein. Here we show that the ΦX174 pilot protein H oligomerizes to form a tube whose function is most probably to deliver the DNA genome across the host's periplasmic space to the cytoplasm. The 2.4 Å resolution crystal structure of the in vitro assembled H protein's central domain consists of a 170 Å-long α-helical barrel. The tube is constructed of ten α-helices with their amino termini arrayed in a right-handed super-helical coiled-coil and their carboxy termini arrayed in a left-handed super-helical coiled-coil. Genetic and biochemical studies demonstrate that the tube is essential for infectivity but does not affect in vivo virus assembly. Cryo-electron tomograms show that tubes span the periplasmic space and are present while the genome is being delivered into the host cell's cytoplasm. Both ends of the H protein contain transmembrane domains, which anchor the assembled tubes into the inner and outer cell membranes. The central channel of the H-protein tube is lined with amide and guanidinium side chains. This may be a general property of viral DNA conduits and is likely to be critical for efficient genome translocation into the host.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacteriophage phi X 174 / chemistry*
  • Bacteriophage phi X 174 / metabolism*
  • Bacteriophage phi X 174 / ultrastructure
  • Biological Transport
  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • Cytoplasm / metabolism
  • Cytoplasm / ultrastructure
  • Cytoplasm / virology
  • DNA, Viral / metabolism*
  • DNA, Viral / ultrastructure
  • Escherichia coli / cytology
  • Escherichia coli / ultrastructure
  • Escherichia coli / virology*
  • Genome, Viral
  • Models, Molecular
  • Periplasm / metabolism
  • Periplasm / ultrastructure
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Viral Proteins / chemistry
  • Viral Proteins / metabolism
  • Viral Proteins / ultrastructure
  • Virus Assembly*


  • DNA, Viral
  • Viral Proteins

Associated data

  • PDB/4JPN
  • PDB/4JPP