Functions of the largest HSV-1 virion protein, pUL36

Herpesviruses are major human pathogens that cause life-long persistent infections and result in clinical manifestations that range from a mild cold sore to cancer. Herpes simplex virus (HSV) is among the most frequently encountered pathogen by the general population. Infection with HSV-1 often results in oralabial disease but it can also cause ocular disease (keratitis) that can lead to blindness or encephalitis, which can be fatal. Type-2 infections are characterized by genital ulcerative disease and infections of the newborn. There is a concerted effort to develop new compounds that block the replication of the virus or a vaccine that can prevent disease. Drugs are being developed that not only target the DNA replication enzymes but also other aspects of the virus life cycle that are amenable to inhibition. The herpesvirus virion is comprised of four structural components: an icosahedral capsid, which encloses the viral DNA genome; an electron dense asymmetrically distributed material, which immediately surrounds the capsid and is termed the tegument; and an outer membrane or envelope, which encloses the tegument and capsid and in which are embedded the viral glycoproteins. Maturation of the capsid into an infectious particle is an essential process and thus potentially a step that can be blocked using a drug or inhibitor. The UL36 gene product is the focus of this proposal. The pUL36 protein, which is resident in the inner-tegument is essential for virus maturation, in its absence, capsids are packaged with genomic DNA and even exit the nucleus (primary envelopment) but subsequently fail to undergo secondary envelopment. This large protein of 336 kDa encodes multiple functions and activities and the protein domains of many of these functions have been mapped and examined in detail. The premise and impetus for undertaking this study, is the observation in preliminary experiments of mutations in UL36 that allow virion morphogenesis. These completely enveloped particles are non-infectious. We will rely on our strength and experience in molecular genetics and cell biological approaches to begin to delineate the impact of these types of mutations on pUL36 activities. Hence, the goal of this proposal is to delineate sites of this protein that could shed light on how pUL36 functions beyond cytoplasmic envelopment. This project is limited to completion of these studies for an important viral protein and satisfies the criteria of an R03 small grant format. The Specific Aims proposed to achieve these goals are: Specific Aim 1: Discover mutant sites in pUL36 that result in the formation non-infectious enveloped virus. Specific Aim 2: Discover how pUL36 functions post-morphogenesis.