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Structure. 2011 Apr 13;19(4):496-502. doi: 10.1016/j.str.2011.02.010.

Peering down the barrel of a bacteriophage portal: the genome packaging and release valve in p22.

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Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA 92093-0378, USA.

Erratum in

  • Structure. 2011 May 11;19(5):748. Olia, Adam [corrected to Olia, Adam S].


The encapsidated genome in all double-strand DNA bacteriophages is packaged to liquid crystalline density through a unique vertex in the procapsid assembly intermediate, which has a portal protein dodecamer in place of five coat protein subunits. The portal orchestrates DNA packaging and exit, through a series of varying interactions with the scaffolding, terminase, and closure proteins. Here, we report an asymmetric cryoEM reconstruction of the entire P22 virion at 7.8 Å resolution. X-ray crystal structure models of the full-length portal and of the portal lacking 123 residues at the C terminus in complex with gene product 4 (Δ123portal-gp4) obtained by Olia et al. (2011) were fitted into this reconstruction. The interpreted density map revealed that the 150 Å, coiled-coil, barrel portion of the portal entraps the last DNA to be packaged and suggests a mechanism for head-full DNA signaling and transient stabilization of the genome during addition of closure proteins.

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