Identification of cellular factors involved in herpes simplex virus type 1 nucelar egress

The herpesvirus life cycle involves a step where newly formed capsids leave the nucleus by translocating across the intact nuclear envelope (NE). Little is known about the role of cellular factors during nuclear egress. We sought to identify novel cellular proteins that interact with the conserved herpes simplex virus-1 (HSV-1) pUL34 by performing a yeast two-hybrid screen. pUL34 was chosen due to its crucial and multifunctional role during nuclear egress. From 42 cellular factors that interacted with pUL34 in yeast, twelve were further evaluated in mammalian cells by co-localization studies using immunofluorescence. No specific co-location between the tested cellular factors and pUL34 was observed in infected cells, thus the screen failed to convincingly identify novel pUL34 interactors. In the second part of the thesis we addressed the functional significance of the cellular protein torsinA (TA) in the HSV-1 life cycle. We became interested in TA due to its role in maintaining normal NE morphology. We showed that perturbing the normal function of TA through overexpression impaired HSV-1 replication and caused a defect in capsid nuclear egress. In mouse embryonic fibroblasts that failed to express TA (TA-/-MEFs), HSV-1 replication was also inhibited, but a defect in capsid nuclear egress was not apparent. Strikingly, infection in TA-null MEFs induced a NE breakdown, the extent of which was dependent on viral products involved in nuclear egress. The viral growth defect and NE envelope breakdown, however, seem to be TA-null cell line specific rather than a functional consequence of TA loss as indicated by TA-/-MEFs reconstituted with TA and 293T with reduced TA levels. In conclusion, overexpression and loss of TA have different effects on the HSV-1 life cycle.