Chapter

Viral Molecular Machines

Volume 726 of the series Advances in Experimental Medicine and Biology pp 585-600

Date:

Genome Gating in Tailed Bacteriophage Capsids

  • Paulo TavaresAffiliated withUnité de Virologie Moléculaire et Structurale, UPR CNRS 3296IFR 115, Bâtiment 14B, CNRS Email author 
  • , Sophie Zinn-JustinAffiliated withLaboratoire de Biologie Structurale et Radiobiologie, iBiTec-SURA CNRS 2096, Bâtiment 144, CEA Saclay
  • , Elena V. OrlovaAffiliated withCrystallography and Institute of Structural and Molecular Biology, Birkbeck College

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Abstract

Tailed bacteriophages use a portal system for genome entry and exit from viral capsids. Here, we review the mechanisms how these movements are controlled by the genome gatekeeper that assembles at the portal structure. Phage DNA is packaged at high pressure inside the viral capsid by a powerful motor. The viral genome is translocated through the central channel of the portal protein found at a single vertex of the capsid. Packaging is normally terminated by endonucleolytic cleavage of the substrate DNA followed by disassembly of the packaging motor and closure of the portal system, preventing leakage of the viral genome. This can be achieved either by conformational changes in the portal protein or by sequential addition of proteins that extend the portal channel (adaptors) and physically close it preventing DNA exit (stoppers). The resulting connector structure provides the interface for assembly of short tails (podoviruses) or for attachment of preformed long tails (siphoviruses and myoviruses). The connector maintains the viral DNA correctly positioned for ejection that is triggered by interaction of the phage particle with bacterial receptors. Recent exciting advances are providing new molecular insights on the mechanisms that ensure precise coordination of these critical steps required both for stable viral genome packaging and for its efficient release to initiate infection.