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Assembly architecture and DNA binding of the bacteriophage P22 terminase small subunit

Academic Article
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Overview

related to degree

  • Lander, Gabriel, Ph.D. in Biophysics, Scripps Research 2004 - 2009

authors

  • Nemecek, D.
  • Lander, Gabriel
  • Johnson Jr., John
  • Casjens, S. R.
  • Thomas, G. J.

publication date

  • November 2008

journal

  • Journal of Molecular Biology  Journal

abstract

  • Morphogenesis of bacteriophage P22 involves the packaging of double-stranded DNA into a preassembled procapsid. DNA is translocated by a powerful virally encoded molecular motor called terminase, which comprises large (gp2, 499 residues) and small (gp3, 162 residues) subunits. While gp2 contains the phosphohydrolase and endonuclease activities of terminase, the function of gp3 may be to regulate specific and nonspecific modes of DNA recognition as well as the enzymatic activities of gp2. Electron microscopy shows that wild-type gp3 self-assembles into a stable and monodisperse nonameric ring. A three-dimensional reconstruction at 18 A resolution provides the first glimpse of P22 terminase architecture and implies two distinct modes of interaction with DNA-involving a central channel of 20 A diameter and radial spikes separated by 34 A. Electromobility shift assays indicate that the gp3 ring binds double-stranded DNA nonspecifically in vitro via electrostatic interactions between the positively charged C-terminus of gp3 (residues 143-152) and phosphates of the DNA backbone. Raman spectra show that nonameric rings formed by subunits truncated at residue 142 retain the subunit fold despite the loss of DNA-binding activity. Difference density maps between gp3 rings containing full-length and C-terminally truncated subunits are consistent with localization of residues 143-152 along the central channel of the nonameric ring. The results suggest a plausible molecular mechanism for gp3 function in DNA recognition and translocation.

subject areas

  • Bacteriophage P22
  • DNA
  • DNA-Binding Proteins
  • Endodeoxyribonucleases
  • Models, Molecular
  • Protein Folding
  • Protein Structure, Tertiary
  • Protein Subunits
  • Viral Proteins
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Research

keywords

  • DNA binding
  • P22 bacteriophage
  • Raman spectroscopy
  • electron microscopy
  • terminase structure
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Identity

PubMed Central ID

  • PMC2577774

International Standard Serial Number (ISSN)

  • 0022-2836

Digital Object Identifier (DOI)

  • 10.1016/j.jmb.2008.08.050

PubMed ID

  • 18775728
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Additional Document Info

start page

  • 494

end page

  • 501

volume

  • 383

issue

  • 3

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