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.
Importance: Like 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.