Herpesviruses are ubiquitous pathogens infecting a wide range of hosts. They exhibit a biphasic lifecycle comprised of a lytic replicative stage and a relatively dormant latent stage. Members of the gammaherpesvirus subfamily include the human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, the etiologic agents of some of the most common AIDS-associated malignancies. During a lytic gammaherpesvirus infection, cellular gene expression is severely compromised in a process termed host shutoff. In this study, we address the purpose of this activity in the viral lifecycle through the generation of a single amino acid point mutant selectively defective for host shutoff activity. Unexpectedly, host shutoff appears largely dispensable for viral replication, yet plays an important role in the ability of the virus to traffic and establish latency in the host organism. These findings link two distinct phases of the viral lifecycle and indicate that the global manipulation of gene expression may contribute to the establishment of a lifelong gammaherpesvirus infection. and MR infections reduced endogenous b-actin (actB), tubulin-b (tubb5), rplp2, and gapdh mRNA levels to 20-40% of the mock infected sample. In contrast, mRNA levels remained significantly higher in MHV68.DHS infected cells ( Figure 3A-3D) . Thus, the single amino acid change R443I in muSOX is sufficient to suppress virus-induced endogenous mRNA turnover. The somewhat lower endogenous mRNA levels in MHV68.DHS compared to mock infected cells could be due either to incomplete inactivation of the muSOX host shutoff function, or to the contribution of one or more additional viral genes towards host shutoff.