Internal proteins of bacteriophage T7

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Abstract

Using electron microscopy it has been shown that there is a protein-containing structure (core) inside bacteriophage T7 which is surrounded by DNA. A similar core is found inside two different DNA-free T7 capsids‡Any structure tha contains a protein envelope related to the envelope which surrounds DNA in T7 phage will be referred to as a capsid. A capsid may or may not have proteins in addition to envelope proteins. isolated from lysates of T7-infected Escherichia coli. One of these capsids (capsid I) appears to play an important role in DNA packaging. Stereo electron microscopy has been used to show that the cores inside capsid I particles closely approximate cylinders with an axial hole. At higher resolution some cores appear to be made of discs of subunits arranged perpendicular to the core axis. Evidence is presented indicating that the core is attached to the outer envelope of the T7 capsids and T7 phage. The core in T7 phage is joined to the outer envelope at the same place as the tail. When DNA is released from T7 phage using heat shock, two types of DNA-free capsid are formed; one has no tail (capsid IVA) and the second has a tail (capsid IVB). Capsids IVA and IVB do not have cores. By comparing the protein compositions of T7 phage, the various T7 capsids and T7 tails, it has been shown that proteins P13, P14, P15 and P16§§Proteins coded for by an identified gene will be designated by P followed by the gene number as determined by comparison with the gel patterns presented by Studier (1972). Proteins which have not yet been assigned genes are designated by capital letters. are possible components of the core. The protein common to the T7 head, core and tail appears to be P8. Core proteins are also found in some of the capsid-DNA complexes described by Serwer (1974a,b). Evidence is presented indicating that the major protein of the envelope of T7, P10, is involved in binding DNA to capsids.

Original languageEnglish (US)
Pages (from-to)271-291
Number of pages21
JournalJournal of Molecular Biology
Volume107
Issue number3
DOIs
StatePublished - Nov 5 1976

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ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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