Packaging of the Virion Host Shutoff (Vhs) Protein of Herpes Simplex Virus: Two Forms of the Vhs Polypeptide Are Associated with Intranuclear B and C Capsids, but Only One Is Associated with Enveloped Virions

Herpesviruses have evolved a unique mechanism for nuclear egress of nascent progeny nucleocapsids: the nucleocapsids bud through the inner nuclear membrane into the perinuclear space between the inner and outer nuclear membranes (primary envelopment), and enveloped nucleocapsids then fuse with the outer nuclear membrane to release nucleocapsids into the cytoplasm (de-envelopment). We have shown that the herpes simplex virus 1 (HSV-1) major virion structural protein UL47 (or VP13/VP14) is a novel regulator for HSV-1 nuclear egress. In particular, we demonstrated the following: (i) UL47 formed a complex(es) with HSV-1 proteins UL34, UL31, and/or Us3, which have all been reported to be critical for viral nuclear egress, and these viral proteins colocalized at the nuclear membrane in HSV-1-infected cells; (ii) the UL47-null mutation considerably reduced primary enveloped virions in the perinuclear space although capsids accumulated in the nucleus; and (iii) UL47 was detected in primary enveloped virions in the perinuclear space by immunoelectron microscopy. These results suggested that UL47 promoted HSV-1 primary envelopment, probably by interacting with the critical HSV-1 regulators for viral nuclear egress and by modulating their functions. IMPORTANCELike other herpesviruses, herpes simplex virus 1 (HSV-1) has evolved a vesicle-mediated nucleocytoplasmic transport mechanism for nuclear egress of nascent progeny nucleocapsids. Although previous reports identified and characterized several HSV-1 and cellular proteins involved in viral nuclear egress, complete details of HSV-1 nuclear egress remain to be elucidated. In this study, we have presented data suggesting (i) that the major HSV-1 virion structural protein UL47 (or VP13/VP14) formed a complex with known viral regulatory proteins critical for viral nuclear egress and (ii) that UL47 played a regulatory role in HSV-1 primary envelopment. Thus, we identified UL47 as a novel regulator for HSV-1 nuclear egress.M orphogenesis of herpes simplex virus 1 (HSV-1), like that of other herpesviruses, takes place in two different cellular compartments (1, 2). Viral DNA replication and transcription, capsid assembly, and packaging of nascent progeny virus genomes into preformed capsids take place in the nucleus, and final envelopment takes place in the cytoplasm (1, 2). Since herpesvirus nucleocapsids are too large to traverse the nuclear lamina or cross the inner and outer nuclear membranes (INM and ONM, respectively) through nuclear pores, these viruses appear to have evolved a unique nuclear egress mechanism in which progeny nucleocapsids acquire primary envelopes by budding through the INM into the space between the INM and ONM, the perinuclear space, and then the enveloped nucleocapsids fuse with the ONM to release de-enveloped nucleocapsids into the cytoplasm (1, 2).In the present study, we focus on the first step of HSV-1 nuclear egress, the process by which progeny nucleocapsids acquire primary envelopes by budding through the INM into the perinuclear space (...

Section: Figcontrasting

confidence: 47%

Herpes Simplex Virus 1 UL47 Interacts with Viral Nuclear Egress Factors UL31, UL34, and Us3 and Regulates Viral Nuclear Egress

Liu

Kato

Shindo

et al. 2014

“…This model of virion egress suggests opportunities for a subset of tegument proteins to attach directly or indirectly to the nucleocapsid in either the nucleosol or cytosol or during budding into nuclear or cytoplasmic membranes. Supporting the idea that at least some tegumentation occurs in the nucleoplasm are the observations that pU L 36, pU L 37, and vhs (the U L 41 gene product) are associated with intranuclear capsids (5,30). Budding through the INM likely causes incorporation of another set of proteins into the tegument, including the peripheral membrane proteins pU L 11 and pU L 31, the viral kinase encoded by U S 3, and the nucleoplasmic proteins VP16 and VP22 (encoded by U L 48 and U L 49, respectively) (2,27,29,31).…”

mentioning

confidence: 63%

The Capsid Protein Encoded by U _L 17 of Herpes Simplex Virus 1 Interacts with Tegument Protein VP13/14

Scholtes

Yang

et al. 2010

Herpesvirus virions are composed of a double-stranded DNA genome encapsidated in an icosahedral shell, an amorphous proteinaceous network surrounding the capsid termed the tegument, and a glycoprotein-decorated envelope surrounding the tegument (reviewed in references 25 and 35). The predominant model of virion assembly involves primary envelopment of the nucleocapsid at the inner nuclear membrane (INM), fusion of this nascent virion envelope with the outer nuclear membrane (ONM), and subsequent attachment of tegument proteins to the de-enveloped nucleocapsid in a region of the cytoplasm derived from the Golgi apparatus and/or transGolgi network (25,34). The fact that the bulk of the tegument is applied at a step after primary envelopment is consistent with the relatively sparse electron microscopic appearance of the perinuclear virion tegument as opposed to the denser tegument of the extracellular virion (3,15). This model of virion egress suggests opportunities for a subset of tegument proteins to attach directly or indirectly to the nucleocapsid in either the nucleosol or cytosol or during budding into nuclear or cytoplasmic membranes. Supporting the idea that at least some tegumentation occurs in the nucleoplasm are the observations that pU L 36, pU L 37, and vhs (the U L 41 gene product) are associated with intranuclear capsids (5, 30). Budding through the INM likely causes incorporation of another set of proteins into the tegument, including the peripheral membrane proteins pU L 11 and pU L 31, the viral kinase encoded by U S 3, and the nucleoplasmic proteins VP16 and VP22 (encoded by U L 48 and U L 49, respectively) (2, 27, 29, 31). Of these, only the pU L 31 gene product is absent from extracellular virions, indicating its loss at the de-envelopment step (13,22,31).

“…We also cannot rule out that these differences are due to the presence of L-particles in the extracellular virus preparations, which may change the relative abundance of some tegument proteins compared to VP5. However, the prospect of a dynamic tegument is a stimulating option that has been reported by others, including a recent report documenting the maturation of the tegument (51,56,115,117,118).…”

Section: Discussionmentioning

confidence: 99%

“…U S 3 thus is one of the early tegument proteins recruited onto capsids, while the U L 31 and U L 34 viral proteins are quickly shed from the capsids. Similarly, both the U L 41 and U L 49 tegument proteins were identified in mature virions and perinuclear virions (8,50,51) and qualify as early tegument proteins.…”

mentioning

confidence: 99%

Analysis of the Early Steps of Herpes Simplex Virus 1 Capsid Tegumentation

Henaff

Rémillard-Labrosse

Loret

et al. 2013

Herpes simplex virus type 1 particles are multilayered structures with a DNA genome surrounded by a capsid, tegument, and envelope. While the protein content of mature virions is known, the sequence of addition of the tegument and the intracellular compartments where this occurs are intensely debated. To probe this process during the initial stages of egress, we used two approaches: an in vitro nuclear egress assay, which reconstitutes the exit of nuclear capsids to the cytoplasm, and a classical nuclear capsid sedimentation assay. As anticipated, in vitro cytoplasmic capsids did not harbor U L 34, U L 31, or viral glycoproteins but contained U S 3. In agreement with previous findings, both nuclear and in vitro capsids were positive for ICP0 and ICP4. Unexpectedly, nuclear C capsids and cytoplasmic capsids produced in vitro without any cytosolic viral proteins also scored positive for U L 36 and U L 37. Immunoelectron microscopy confirmed that these tegument proteins were closely associated with nuclear capsids. When cytosolic viral proteins were present in the in vitro assay, no additional tegument proteins were detected on the capsids. As previously reported, the tegument was sensitive to high-salt extraction but, surprisingly, was stabilized by exogenous proteins. Finally, some tegument proteins seemed partially lost during egress, while others possibly were added at multiple steps or modified along the way. Overall, an emerging picture hints at the early coating of capsids with up to 5 tegument proteins at the nuclear stage, the shedding of some viral proteins during nuclear egress, and the acquisition of others tegument proteins during reenvelopment.