Expression and purification of phage T7 ejection proteins for cryo-EM analysis

STAR Protoc. 2021 Nov 16;2(4):100960. doi: 10.1016/j.xpro.2021.100960. eCollection 2021 Dec 17.


Bacteriophages of the Podoviridae family densely package their genomes into precursor capsids alongside internal virion proteins called ejection proteins. In phage T7 these proteins (gp14, gp15, and gp16) are ejected into the host envelope forming a DNA-ejectosome for genome delivery. Here, we describe the purification and characterization of recombinant gp14, gp15, and gp16. This protocol was used for high-resolution cryo-EM structure analysis of the T7 periplasmic tunnel and can be adapted to study ejection proteins from other phages. For complete details on the use and execution of this protocol, please refer to Swanson et al. (2021).

Keywords: Cryo-EM; Microbiology; Microscopy; Protein Biochemistry; Protein expression and purification; Structural Biology.

Publication types

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

MeSH terms

  • Bacteriophage T7* / genetics
  • Bacteriophage T7* / metabolism
  • Cryoelectron Microscopy / methods*
  • Escherichia coli / genetics
  • Periplasm / chemistry
  • Periplasm / metabolism
  • Recombinant Proteins* / chemistry
  • Recombinant Proteins* / genetics
  • Recombinant Proteins* / isolation & purification
  • Recombinant Proteins* / metabolism
  • Viral Proteins* / chemistry
  • Viral Proteins* / genetics
  • Viral Proteins* / isolation & purification
  • Viral Proteins* / metabolism


  • Recombinant Proteins
  • Viral Proteins