Role of the UL25 gene product in packaging DNA into the herpes simplex virus capsid: Location of UL25 product in the capsid and demonstration that itbinds DNA

Recent studies have suggested that the herpes simplex type 1 (HSV-1) UL25 g ene product, a minor capsid protein, is required for encapsidation but not cleavage of replicated viral DNA. This study set out to investigate the pot ential interactions of UL25 protein with other virus proteins and determine what properties it has for playing a role in DNA encapsidation. The UL25 p rotein is found in 42 +/- 17 copies per B capsid and is present in both pen tons and herons. We introduced green fluorescent protein (GFP) as a fluores cent tag into the N terminus of UL25 protein to identify its location in HS V-1-infected cells and demonstrated the relocation of UL25 protein from the cytoplasm into the nucleus at the late stage of HSV-1 infection. To clarif y the cause of this relocation, we analyzed the interactions of UL25 protei n with other virus proteins. The UL25 protein associates with VP5 and VP19C of virus capsids, especially of the penton structures, and the association with VP19C causes its relocation into the nucleus. Gel mobility shift anal ysis shows that UL25 protein has the potential to bind DNA. Moreover, the a mino-terminal one-third of the UL25 protein is particularly important in DN A binding and forms a homo-oligomer. In conclusion, the UL25 gene product f orms a tight connection with the capsid being linked with VP5 and VP19C, an d it may play a role in anchoring the genomic DNA.