Small terminase couples viral DNA binding to genome-packaging ATPase activity

Structure. 2012 Aug 8;20(8):1403-13. doi: 10.1016/j.str.2012.05.014. Epub 2012 Jul 5.


Packaging of viral genomes into empty procapsids is powered by a large DNA-packaging motor. In most viruses, this machine is composed of a large (L) and a small (S) terminase subunit complexed with a dodecamer of portal protein. Here we describe the 1.75 Å crystal structure of the bacteriophage P22 S-terminase in a nonameric conformation. The structure presents a central channel ∼23 Å in diameter, sufficiently large to accommodate hydrated B-DNA. The last 23 residues of S-terminase are essential for binding to DNA and assembly to L-terminase. Upon binding to its own DNA, S-terminase functions as a specific activator of L-terminase ATPase activity. The DNA-dependent stimulation of ATPase activity thus rationalizes the exclusive specificity of genome-packaging motors for viral DNA in the crowd of host DNA, ensuring fidelity of packaging and avoiding wasteful ATP hydrolysis. This posits a model for DNA-dependent activation of genome-packaging motors of general interest in virology.

Publication types

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

MeSH terms

  • Adenosine Triphosphate / chemistry
  • Amino Acid Sequence
  • Bacteriophage P22 / enzymology*
  • Bacteriophage P22 / physiology
  • Binding Sites
  • Crystallography, X-Ray
  • DNA, Viral / chemistry
  • Endodeoxyribonucleases / chemistry*
  • Hydrolysis
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Protein Subunits / chemistry
  • Viral Proteins / chemistry*
  • Virus Assembly*


  • DNA, Viral
  • Protein Subunits
  • Viral Proteins
  • Adenosine Triphosphate
  • Endodeoxyribonucleases
  • terminase

Associated data

  • PDB/3P9A