Visualization of tegument-capsid interactions and DNA in intact herpes simplex virus type 1 virions

Herpes simplex virus type 1 virions were examined by electron cryomicroscop y, allowing the three-dimensional structure of the infectious particle to b e visualized for the first time. The capsid shell is identical to that of B -capsids purified from the host cell nucleus, with the exception of the pen ton channel, which is closed. The double-stranded DNA genome is organized a s regularly spaced (similar to 26 Angstrom) concentric layers inside the ca psid. This pattern suggests a spool model for DNA packaging, similar to tha t for some bacteriophages. The bulk of the tegument is not icosahedrally or dered. However, a small portion appears as filamentous structures around th e pentons, interacting extensively with the capsid. Their locations and int eractions suggest possible roles for the tegument proteins in regulating DN A transport through the penton channel and binding to cellular transport pr oteins during viral infection.