B virus (Cercopithecine herpesvirus 1), which causes an often fatal zoonotic infection in humans, shares extensive homology with human herpes simplex virus type 1 (HSV-1). The ƒ×134.5 gene of HSV-1 plays a major role in counteracting dsRNA-dependent protein kinase (PKR) activity. HSV-1 Us11 protein, if expressed early as a result of mutation, binds to PKR and prevents PKR activation. The results of experiments in this dissertation revealed that although B virus lacks a ƒ×134.5 gene homolog, it is able to inhibit PKR activation, and subsequently, eIF2ƒÑ phosphorylation. The initial hypothesis was that B virus Us11 protein substitutes for the function of ƒ×134.5 gene homolog by blocking cellular PKR activation. Using western blot analysis, Us11 protein (20 kDa) of B virus was observed early following infection (3 h post infection). Expression of B virus Us11 protein was not blocked by phosphonoacetic acid (PAA), an inhibitor of DNA replication, confirming Us11 is not a ¡§true late¡¨ gene of B virus as it is in HSV-1. Analysis of these results suggested that B virus Us11 protein compensates for the lack of the ƒ×134.5 gene homolog and prevents PKR activation. Next, the results demonstrated that B virus Us11 recombinant protein prevented PKR activation by dsRNA in vitro. A B virus Us11 protein stable expression cell line (U373-BVUs11) was established to investigate whether Us11 protein inhibited PKR activation in vivo. Experiments revealed that B virus Us11 protein stably expressed in U373 cells prevented PKR activation and subsequent eIF2ƒÑ phosphorylation induced by the infection of these cells with ƒ´ƒ×134.5 of HSV-1. As the consequence of preventing PKR activation and subsequent eIF2ƒÑ phosphorylation, B virus Us11 protein complemented ƒ´ƒ×134.5 HSV-1 in U373 cells as evidenced by restoration of virus protein synthesis and replication in U373 cells. Furthermore, pull-down assays showed that B virus Us11 protein binds to PKR. In addition, the results demonstrated that B virus Us11 protein stably expressed in U373 cells counteracted the inhibiting effect of IFN-ƒÑ on HSV-1 replication by preventing PKR activation. These data suggested that B virus and HSV-1, two closely related viruses, use different mechanisms to counteract PKR activity.

Microplitis croceipes is a solitary endoparasitic wasp that oviposits in the hemocoel of Heleothis virescens larvae. Upon parasitization, the host larvaes physiology is altered; resulting in a compromised immune system and a decrease in the production of some vital proteins resulting in a terminal post-wandering prepupal state. Teratocytes, cells derived from the extraembryonic serosa of the parasitic wasp, mimic symptoms of parasitization when injected into host larvae, independent of other factors like polydnavirus and venom. Some of the inhibition of protein synthesis can be attributed to proteins secreted by the teratocytes (teratocyte secretory proteins or TSP). A fraction of TSP between 330 kDa inhibits protein synthesis in vivo, in the in vitro fat body and testes assays, and in the rabbit reticulocyte lysate and wheat germ extract assays. This fraction, however, has no effect on nucleic acid synthesis. Its effect on protein synthesis is dose dependent and exposure time sensitive. A 13.9 kDa protein isolated from TSP and expressed in a baculovirus system seems primarily responsible for the inhibition. Although TSP14 production was low, it did bind to the cell surface, enter the cell, and inhibit protein synthesis as the 330 kDa factor did.