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Human cytomegalovirus (HCMV) pUL93 is essential for virus growth, but its precise function in the virus life cycle is unknown. Here, we characterize a UL93 stop mutant virus (UL93st-TB40/E-BAC) to demonstrate that the absence of this protein does not restrict viral gene expression; however, cleavage of viral DNA into unit-length genomes as well as genome packaging is abolished. Thus, pUL93 is required for viral genome cleavage and packaging.H uman cytomegalovirus (HCMV) protein pUL93, a putative tegument protein, is required for the growth of HCMV (1, 2), but the exact function of this protein is unknown. There is no functional study done to date on HCMV pUL93; however, pUL17, the positional homolog of pUL93 in herpes simplex virus 1 (HSV-1), has been shown to be required for the localization of capsids to the DNA replication compartments in the infected cell nucleus, where viral genome cleavage and packaging take place (3, 4). pUL17 has also been found to interact with pUL25, a homolog of HCMV pUL77, to form the capsid vertex-specific component (CVSC), which is found at the 12 vertices of the icosahedral capsid (4-10). The exact function of the CVSC is currently unknown, but it is thought to aid in capsid stability and nuclear egress (10-13). pUL25-null mutants package viral DNA only transiently and produce mostly empty capsids, while pUL17-null mutants completely abolish DNA packaging (3,14). It is important to note that pUL17 and pUL93 are positional homologs that share only 1.5% sequence identity, 1.9% sequence similarity, and no distinct conserved domains (based on amino acid ClustalW alignment). Moreover, several HCMV proteins have been found to have very different functions compared to their homologs in other herpesviruses, highlighting the importance of studying HCMV proteins independently. For example, HCMV pUL50 and pUL53 were presumed to recruit host protein kinase C (PKC) for disruption of the nuclear lamina based on data from other herpesviruses but were instead found to recruit viral protein kinase pUL97 for this purpose (15). Targeting of essential structural viral proteins holds great promise for the development of antivirals that would be highly specific and effective and also less susceptible to the development of resistance be- Citation DeRussy BM, Tandon R. 2015. Human cytomegalovirus pUL93 is required for viral genome cleavage and packaging.

West Nile virus is a pathogen of concern for both human and wildlife health. Although many aspects of the ecology of West Nile virus are well understood, the mechanisms by which this and similar mosquito-borne viruses overwinter and become reinitiated each spring in temperate regions is not known. A thorough understanding of this mechanism is crucial to risk assessment and development of control strategies. One of the hypotheses to explain the mechanism by which this virus persists from year to year is the spring recrudescence of latent virus in avian reservoir hosts. Stress-related immunosuppression is implicated in the recrudescence of latent viruses in birds. We tested the spring recrudescence hypothesis in a controlled laboratory experiment using hatching-year gray catbirds (Dumatella carolinensis) captured in northern Ohio (July-August 2006). Catbirds (n = 60) were experimentally infected (September 2006) and later examined for the effects of immunosuppression through exogenous hormones and artificially induced migratory disposition. We found no effect of either testosterone or migratory behavior on infection status in any of the treatment birds. Moreover, we detected no viral RNA in the kidney, spleen, brain, or liver upon necropsy at 24 wk postinfection.

Human cytomegalovirus (HCMV) pUL93 and pUL77 are both essential for virus growth, but their functions in the virus life cycle remain mostly unresolved. Homologs of pUL93 and pUL77 in herpes simplex virus 1 (HSV-1) and pseudorabies virus (PRV) are known to interact to form a complex at capsid vertices known as the capsid vertex-specific component (CVSC), which likely stabilizes nucleocapsids during virus maturation and also aids in nuclear egress. In herpesviruses, nucleocapsids assemble and partially mature in nuclear replication compartments and then travel to the inner nuclear membrane (INM) for nuclear egress. The factors governing the recruitment of nucleocapsids to the INM are not known. Kinetic analysis of pUL93 demonstrates that this protein is expressed late during infection and localizes primarily to the nucleus of infected cells. pUL93 associates with both virions and capsids and interacts with the components of the nuclear egress complex (NEC), namely, pUL50, pUL53, and pUL97, during infection. Also, multiple regions in pUL93 can independently interact with pUL77, which has been shown to help retain viral DNA during capsid assembly. These studies, combined with our earlier report of an essential role of pUL93 in viral DNA packaging, indicate that pUL93 serves as an important link between nucleocapsid maturation and nuclear egress. IMPORTANCEHCMV causes life-threatening disease and disability in immunocompromised patients and congenitally infected newborns. In this study, we investigated the functions of HCMV essential tegument protein pUL93 and determined that it interacts with the components of the nuclear egress complex, namely, pUL50, pUL53, and pUL97. We also found that pUL93 specifically interacts with pUL77, which helps retain viral DNA during capsid assembly. Together, our data point toward an important role of pUL93 in linking virus maturation to nuclear egress. In addition to expanding our knowledge of the process of HCMV maturation, information from these studies will also be utilized to develop new antiviral therapies. In herpes simplex virus 1 (HSV-1) and pseudorabies virus (PRV), pUL17 and pUL25, the homologs of human cytomegalovirus (HCMV) pUL93 and pUL77, respectively, form a complex called the capsid vertex-specific component (CVSC) (1-5). Five copies of this complex surround each of the 12 vertices of the capsids. This complex was originally termed the C-capsid-specific component (2) based on its presence on DNA containing C-capsids, but it was later found to be present on all capsid types (1). Nevertheless, some differences have been reported in the relative distribution of the CVSC on different capsid types in herpesviruses. In HSV-1, occupancy of the CVSC is approximately 50% on C-capsids and only 25% or less on A-(empty) and B-capsids (scaffold containing), while in PRV, occupancy of the CVSC is nearly 100% on C-capsids and 55% on B-capsids (2, 5). The CVSC is thought to aid in DNA packaging and retention by stabilizing capsids during capsid assembly and in nuclear egress,...

Human cytomegalovirus (CMV) is a herpesvirus that causes major health problems in neonates as well as in immunocompromised individuals1. At present, a vaccine is not available for CMV infection and the available antiviral drugs suffer from toxicity, poor efficacy and resistance12. Here, we chemically conjugated a monoclonal antibody raised against CMV surface glycoprotein (gB) with gold nanoparticles (GNP) and characterized the potential of this gB-GNP conjugate for antiviral activity against CMV. The gB-GNP blocks viral replication, virus-induced cytopathogenic effects and virus spread in cell culture without inducing cytotoxicity. High concentrations of gB-GNP that coat the surface of virus particles block virus entry, whereas lower concentrations block a later stage of virus life cycle. Also, cells treated with gB-GNP gain resistance to CMV infection. In addition, infected cells when bound to gB-GNP can be selectively lysed after exposing them to specific wavelength of laser (nanophotothermolysis). Thus, we have not only designed a potential antiviral strategy that specifically blocks CMV infection at multiple stages of virus life cycle, but we have also characterized a technique that can potentially be useful in eliminating CMV infected cells from donor tissue during transplant or transfusion.