Document Detail

Structure and assembly of the capsid of bacteriophage P22.
MedLine Citation:
PMID:  13434     Owner:  NLM     Status:  MEDLINE    
Identification of the genes and proteins involved in phage P22 formation has permitted a detailed analysis of particle assembly, revealing some unexpected aspects. The polymerization of the major coat protein (gene 5 product) into an organized capsid is directed by a scaffolding protein (gene 8 product) which is absent from mature phage. The resulting capsid structure (prohead) is the precursor for DNA encapsidation. All of the scaffolding protein exits from the prohead in association with DNA packaging. These molecules then recycle, directing further rounds of prohead assembly. The structure of the prohead has been studied by electron microscopy of thin sections of phage infected cells, and by low angle X-ray scattering of concentrated particles. The results show that the prohead is a double shell structure, or a ball within a shell. The inner ball or shell is composed of the scaffolding protein while the outer shell is composed of coat protein. The conversion from prohead to mature capsid is associated with an expansion of the coat protein shell. It is possible that the scaffolding protein molecules exit through the capsid lattice. When DNA encapsidation within infected cells is blocked by mutation, scaffolding protein is trapped in proheads and cannot recycle. Under these conditions, the rate of synthesis of gp8 increases, so that normal proheads continue to form. These results suggest that free scaffolding protein negatively regulates its own further synthesis, providing a coupling between protein synthesis and protein assembly.
J King; D Botstein; S Casjens; W Earnshaw; S Harrison; E Lenk
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Philosophical transactions of the Royal Society of London. Series B, Biological sciences     Volume:  276     ISSN:  0962-8436     ISO Abbreviation:  Philos. Trans. R. Soc. Lond., B, Biol. Sci.     Publication Date:  1976 Nov 
Date Detail:
Created Date:  1977-03-21     Completed Date:  1977-03-21     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  7503623     Medline TA:  Philos Trans R Soc Lond B Biol Sci     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  37-49     Citation Subset:  IM    
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MeSH Terms
Capsid* / metabolism
DNA, Viral / biosynthesis
Genetics, Microbial
Salmonella Phages* / metabolism
Salmonella typhimurium* / ultrastructure
Viral Proteins* / biosynthesis,  metabolism
Reg. No./Substance:
0/DNA, Viral; 0/Viral Proteins

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