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J Virol. 2011 Aug;85(15):7513-22. doi: 10.1128/JVI.00837-11. Epub 2011 Jun 1.

The herpes simplex virus 1 UL17 protein is the second constituent of the capsid vertex-specific component required for DNA packaging and retention.

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Department of Structural Biology, University of Pittsburgh, Biomedical Science Tower 3, 3501 5th Ave., Pittsburgh, PA 15260, USA.


The herpes simplex virus (HSV) UL17 and UL25 minor capsid proteins are essential for DNA packaging. They are thought to comprise a molecule arrayed in five copies around each of the capsid vertices. This molecule was initially termed the "C-capsid-specific component" (CCSC) (B. L. Trus et al., Mol. Cell 26:479-489, 2007), but as we have subsequently observed this feature on reconstructions of A, B, and C capsids, we now refer to it more generally as the "capsid vertex-specific component" (CVSC) (S. K. Cockrell et al., J. Virol. 85:4875-4887, 2011). We previously confirmed that UL25 occupies the vertex-distal region of the CVSC density by visualizing a large UL25-specific tag in reconstructions calculated from cryo-electron microscopy (cryo-EM) images. We have pursued the same strategy to determine the capsid location of the UL17 protein. Recombinant viruses were generated that contained either a small tandem affinity purification (TAP) tag or the green fluorescent protein (GFP) attached to the C terminus of UL17. Purification of the TAP-tagged UL17 or a similarly TAP-tagged UL25 protein clearly demonstrated that the two proteins interact. A cryo-EM reconstruction of capsids containing the UL17-GFP protein reveals that UL17 is the second component of the CVSC and suggests that UL17 interfaces with the other CVSC component, UL25, through its C terminus. The portion of UL17 nearest the vertex appears to be poorly constrained, which may provide flexibility in interacting with tegument proteins or the DNA-packaging machinery at the portal vertex. The exposed locations of the UL17 and UL25 proteins on the HSV-1 capsid exterior suggest that they may be attractive targets for highly specific antivirals.

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