Length quantization of DNA partially expelled from heads of a bacteriophage T3 mutant

Philip Serwer, Elena T. Wright, Zheng Liu, Wen Jiang

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


DNA packaging of phages phi29, T3 and T7 sometimes produces incompletely packaged DNA with quantized lengths, based on gel electrophoretic band formation. We discover here a packaging ATPase-free, in vitro model for packaged DNA length quantization. We use directed evolution to isolate a five-site T3 point mutant that hyper-produces tail-free capsids with mature DNA (heads). Three tail gene mutations, but no head gene mutations, are present. A variable-length DNA segment leaks from some mutant heads, based on DNase I-protection assay and electron microscopy. The protected DNA segment has quantized lengths, based on restriction endonuclease analysis: six sharp bands of DNA missing 3.7-12.3% of the last end packaged. Native gel electrophoresis confirms quantized DNA expulsion and, after removal of external DNA, provides evidence that capsid radius is the quantization-ruler. Capsid-based DNA length quantization possibly evolved via selection for stalling that provides time for feedback control during DNA packaging and injection.

Original languageEnglish (US)
Pages (from-to)157-170
Number of pages14
Issue number1
StatePublished - May 2014


  • Agarose gel electrophoresis, native
  • Bacteriophage assembly
  • Capsid structure
  • DNA packaging
  • Mutant phenotype
  • Ultracentrifugation

ASJC Scopus subject areas

  • Virology


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