No abstract

. 83:3115-3126, 2009). In the studies reported here, we examined the effect(s) of this phosphorylation on viral replication and pathogenesis in vivo and present data showing that replacement of gB Thr-887 by alanine significantly reduced viral replication in the mouse cornea and development of herpes stroma keratitis and periocular skin disease in mice. The same effects have been reported for mice infected with a recombinant HSV-1 carrying a kinase-inactive mutant of Us3. These observations suggested that Us3 phosphorylation of gB Thr-887 played a critical role in viral replication in vivo and in HSV-1 pathogenesis. In addition, we generated a monoclonal antibody that specifically reacted with phosphorylated gB Thr-887 and used this antibody to show that Us3 phosphorylation of gB Thr-887 regulated subcellular localization of gB, particularly on the cell surface of infected cells.

Herpes simplex virus 1 (HSV-1) protein VP22, encoded by the UL49 gene, is a major virion tegument protein. In the present study, we showed that VP22 was required for efficient redistribution of viral proteins VP16, VP26, ICP0, ICP4, and ICP27 and of cellular protein Hsc-70 to the cytoplasm of infected cells. We found that two dileucine motifs in VP22, at amino acids 235 and 236 and amino acids 251 and 252, were necessary for VP22 regulation of the proper cytoplasmic localization of these viral and cellular proteins. The dileucine motifs were also required for proper cytoplasmic localization of VP22 itself and for optimal expression of viral proteins VP16, VP22, ICP0, UL41, and glycoprotein B. Interestingly, a recombinant mutant virus with alanines substituted for the dileucines at amino acids 251 and 252 had a 50% lethal dose (LD 50 ) for neurovirulence in mice following intracerebral inoculation about 10 3 -fold lower than the LD 50 of the repaired virus. Furthermore, the replication and spread of this mutant virus in the brains of mice following intracerebral inoculation were significantly impaired relative to those of the repaired virus. The ability of VP22 to regulate the localization and expression of various viral and cellular proteins, as shown in this study, was correlated with an increase in viral replication and neurovirulence in the experimental murine model. Thus, HSV-1 VP22 is a significant neurovirulence factor in vivo. Herpes simplex virus 1 (HSV-1) virions, like those of other herpesviruses, consist of three morphologically distinct structures: the nucleocapsid, containing the linear doublestranded DNA viral genome, which encodes at least 84 viral proteins, in an icosahedral capsid; the tegument, a proteinaceous layer surrounding the nucleocapsid; and the envelope, a host cellderived lipid bilayer with viral glycoproteins enclosing the nucleocapsid and tegument (55). The tegument consists of a large number of proteins, including at least 26 viral proteins (41). Tegument proteins are released into the cytoplasm upon the fusion of the virion envelope with the host cell membrane and therefore may function to establish an environment for effective initiation of very early infection. However, the roles of only a few tegument proteins, including the immediate-early gene transactivator VP16, encoded by the UL48 gene, and the virion host shutoff protein VHS, encoded by the UL41 gene (55), in very early infection have been established. Large amounts of newly synthesized tegument proteins have also been shown to modulate the host cellular environment and to regulate various viral replication processes later in infection (28).VP22, encoded by the UL49 gene, is one of the major HSV-1 tegument proteins, and its amino acid sequence is conserved in the subfamily Alphaherpesvirinae. It appears that the functional requirements of VP22 homologues in the viral life cycle differ among alphaherpesviruses. For example, the VP22 homologues of Marek's disease virus serotype 1 and varicella-zoster virus are considered to...