During herpes simplex virus 1 (HSV-1) replication, newly constructed capsids escape the nucleus to undergo maturation in the cytoplasm via a process termed nuclear egress. Capsids perform nuclear egress through localized disruption of the nuclear lamina, envelopment of the inner nuclear membrane to create a perinuclear enveloped virion, and de-envelopment of the outer nuclear membrane for capsid release into the cytoplasm. Critical virial factors for this process are viral proteins pUL31 and pUL34 that interact to form heterodimers. These heterodimers form larger hexameric arrays to drive membrane budding. Through the
characterization of phenotypes of UL34 point mutants, we are able to further study the underlying mechanisms of nuclear lamina disruption and nuclear budding. One such mutant, UL34(Q163A), results in impaired virus production, cell-cell spread, and an inability to disrupt lamin A/C networks. Selection for extragenic suppression of UL34(Q163A) yielded the UL31(R229L) mutation, that partially rescued the growth and spread defects of UL34(Q163A), but was unable to regain the ability to disrupt lamin A/C networks. Through this study we concluded that disruption of lamin A/C networks was not required for efficient HSV-1 replication. In order to understand the underlying mechanisms of membrane budding, the previously characterized UL34(CL13) double mutant, which results in a 100-fold reduction in virus production, a severe impairment in cell-cell spread, and an accumulation of capsid-less perinuclear vesicles was further studied. Characterization of the single mutations of UL34(CL13), UL34(R158A) and UL34(R161A) revealed that neither single mutation was responsible for spread or growth defect, but that either single mutation resulted in a promiscuous budding phenotype. Through this study, we concluded that although individual steps of the nuclear egress pathway are tightly regulated, alteration of the regulation at a single step does not grossly impact HSV-1 replication.