The UL31 and UL34 Gene Products of Herpes Simplex Virus 1 Are Required for Optimal Localization of Viral Glycoproteins D and M to the Inner Nuclear Membranes of Infected Cells

摘要

UL31 and UL34 of herpes simplex virus type 1 form a complex necessary for nucleocapsid budding at the inner nuclear membrane (INM). Previous examination by immunogold electron microscopy and electron tomography showed that pUL31, pUL34, and glycoproteins D and M are recruited to perinuclear virions and densely staining regions of the INM where nucleocapsids bud into the perinuclear space. We now show by quantitative immunogold electron microscopy coupled with analysis of variance that gD-specific immunoreactivity is significantly reduced at both the INM and outer nuclear membrane (ONM) of cells infected with a UL34 null virus. While the amount of gM associated with the nuclear membrane (NM) was only slightly (P = 0.027) reduced in cells infected with the UL34 null virus, enrichment of gM in the INM at the expense of that in the ONM was greatly dependent on UL34 (P < 0.0001). pUL34 also interacted directly or indirectly with immature forms of gD (species expected to reside in the endoplasmic reticulum or nuclear membrane) in lysates of infected cells and with the cytosolic tail of gD fused to glutathione S-transferase in rabbit reticulocyte lysates, suggesting a role for the pUL34/gD interaction in recruiting gD to the NM. The effects of UL34 on gD and gM localization were not a consequence of decreased total expression of gD and gM, as determined by flow cytometry. Separately, pUL31 was dispensable for targeting gD and gM to the two leaflets of the NM but was required for (i) the proper INM-versus-ONM ratio of gD and gM in infected cells and (ii) the presence of electron-dense regions in the INM, representing nucleocapsid budding sites. We conclude that in addition to their roles in nucleocapsid envelopment and lamina alteration, UL31 and UL34 play separate but related roles in recruiting appropriate components to nucleocapsid budding sites at the INM.