Protein P7 of the cystovirus φ6 is located at the three-fold axis of the unexpanded procapsid

PLoS One. 2012;7(10):e47489. doi: 10.1371/journal.pone.0047489. Epub 2012 Oct 15.


The objective of this study was to determine the location of protein P7, the RNA packaging factor, in the procapsid of the φ6 cystovirus. A comparison of cryo-electron microscopy high-resolution single particle reconstructions of the φ6 complete unexpanded procapsid, the protein P2-minus procapsid (P2 is the RNA directed RNA-polymerase), and the P7-minus procapsid, show that prior to RNA packaging the P7 protein is located near the three-fold axis of symmetry. Difference maps highlight the precise position of P7 and demonstrate that in P7-minus particles the P2 proteins are less localized with reduced densities at the three-fold axes. We propose that P7 performs the mechanical function of stabilizing P2 on the inner protein P1 shell which ensures that entering viral single-stranded RNA is replicated.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriophage phi 6 / genetics
  • Bacteriophage phi 6 / ultrastructure*
  • Capsid / chemistry
  • Capsid / metabolism
  • Capsid / ultrastructure*
  • Cryoelectron Microscopy
  • RNA, Double-Stranded / chemistry
  • RNA, Viral / chemistry
  • RNA, Viral / genetics
  • Viral Proteins / chemistry*
  • Virus Assembly
  • Virus Replication / genetics*


  • RNA, Double-Stranded
  • RNA, Viral
  • Viral Proteins