Comparison of the physical properties and assembly pathways of the related bacteriophages T7, T3 and II

Philip Serwer, Robert H. Watson, Shirley J. Hayes, Jerry L. Allen

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Abstract

To understand constraints on the evolution of bacteriophage assembly, the structures, electrophoretic mobilities (μ) and assembly pathways of the related double-stranded DNA bacteriophages T7, T3 and II, have been compared. The characteristics of the following T7, T3 and II capsids in these assembly pathways have also been compared: (1) a DNA-free procapsid (capsid I) that packages DNA during assembly; (b) a DNA packaging-associated conversion product of capsid I (capsid II). The molecular weights of the T3 and II genomes were 25·2 × 106 and 25·9(±0·2) × 106 (26·44 × 106 for T7, as previously determined), as determined by agarose gel electrophoresis of intact genomes. The radii of T7, T3 and II bacteriophages were indistinguishable by sieving during agarose gel electrophoresis (±4%) and measurement of the bacteriophage hydration (±2%) (30·1 nm for T7, as previously determined). Assuming a T = 7 icosahedral lattice for the arrangement of the major capsid subunits (p10A) of T7, T3 and II best explains these data and data previously obtained for T7. At pH 7·4 and an ionic strength of 1·2, the solid-support-free μ values (μ0 values) of T7, T3 and II bacteriophages, obtained by extrapolation of μ during agarose gel electrophoresis to an agarose concentration of 0 and correction for electro-osmosis, were -0·71, -0·91 and -1·17(× 10-4) cm2V-1s-1. The μ0 values of T7, T3 and II capsids I were -1·51, -1·58 and -2·07(× 10-4)cm2V-1s-1. For the capsids II, these μ0 values were -0·82, -1·07 and -1·37(× 10-4)cm2V-1s-1. The tails of all three bacteriophages were positively charged and the capsid envelopes (heads) were negatively charged. In all cases the procapsid had a negative μ0 value larger in magnitude than the negative μ0 value for bacteriophage or capsid II. A trypsinsensitive region in capsid I-associated, but not capsid II-associated, T3 p10A was observed (previously observed for T7). The largest fragment of trypsinized capsid I-associated p10A had the same molecular weight in T7 and T3, although the T3 p10A is 18% more massive than the T7 p10A. It is suggested that the trypsin-resistant region of capsid I-associated p10A determines the radius of the bacteriophage capsid.

Original languageEnglish (US)
Pages (from-to)447-469
Number of pages23
JournalJournal of Molecular Biology
Volume170
Issue number2
DOIs
Publication statusPublished - Oct 25 1983

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ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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