Abstract
Double-stranded DNA bacteriophages package their genome at high pressure inside a procapsid through the portal, an oligomeric ring protein located at a unique capsid vertex. Once the DNA has been packaged, the tail components assemble on the portal to render the mature infective virion. The tail tightly seals the ejection conduit until infection, when its interaction with the host membrane triggers the opening of the channel and the viral genome is delivered to the host cell. Using high-resolution cryo-electron microscopy and X-ray crystallography, here we describe various structures of the T7 bacteriophage portal and fiber-less tail complex, which suggest a possible mechanism for DNA retention and ejection: a portal closed conformation temporarily retains the genome before the tail is assembled, whereas an open portal is found in the tail. Moreover, a fold including a seven-bladed β-propeller domain is described for the nozzle tail protein.
Highlights
Double-stranded DNA bacteriophages package their genome at high pressure inside a procapsid through the portal, an oligomeric ring protein located at a unique capsid vertex
The portal protein is always found as a dodecamer in virions, assemblies containing 11–13 subunits have been described for other portals when expressed under non-physiological conditions[13,32]
In the case of phage SPP1, rearrangements of the portal protein subunits are essential for DNA translocation[42] and they are related to the interaction with DNA in the inner channel of the portal assembly[23]
Summary
Double-stranded DNA bacteriophages package their genome at high pressure inside a procapsid through the portal, an oligomeric ring protein located at a unique capsid vertex. DNA packaging into preformed proheads requires the interaction of the portal protein with the terminase, which generates forces involved in the processive translocation of dsDNA into the viral capsid, where it is stored at quasi-crystalline concentration[1,14,15]. Both in phages[16,17,18] and in herpesviruses[19], the interaction of the packaging terminase occurs at a region of the portal protein that extends outside the capsid shell through the portal vertex. These observations suggest that this conformational change might be related to the structure before and after assembly in the mature phage[26]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
