The human protein DDX3X is a DEAD box ATP-dependent RNA helicase that regulates transcription, mRNA maturation, and mRNA export and translation. DDX3X concomitantly modulates the replication of several RNA viruses and promotes innate immunity. We previously showed that herpes simplex virus 1 (HSV-1), a human DNA virus, incorporates DDX3X into its mature particles and that DDX3X is required for optimal HSV-1 infectivity. Here, we show that viral gene expression, replication, and propagation depend on optimal DDX3X protein levels. Surprisingly, DDX3X from incoming viral particles was not required for the early stages of the HSV-1 infection, but, rather, the protein controlled the assembly of new viral particles. This was independent of the previously reported ability of DDX3X to stimulate interferon type I production. Instead, both the lack and overexpression of DDX3X disturbed viral gene transcription and thus subsequent genome replication. This suggests that in addition to its effect on RNA viruses, DDX3X impacts DNA viruses such as HSV-1 by an interferon-independent pathway. IMPORTANCE Viruses interact with a variety of cellular proteins to complete their life cycle. Among them is DDX3X, an RNA helicase that participates in most aspects of RNA biology, including transcription, splicing, nuclear export, and translation. Several RNA viruses and a limited number of DNA viruses are known to manipulate DDX3X for their own benefit. In contrast, DDX3X is also known to promote interferon production to limit viral propagation. Here, we show that DDX3X, which we previously identified in mature HSV-1 virions, stimulates HSV-1 gene expression and, consequently, virion assembly by a process that is independent of its ability to promote the interferon pathway. KEYWORDS DDX3X, helicase, herpes, host-pathogen interaction, DNA virus, RNA virus, interferon, herpes simplex virus, host-pathogen interactions, transcriptional regulation, translational control T he human DDX3 protein is a member of a large family of DEAD box ATP-dependent RNA helicases. In humans, it is encoded by the X (DDX3X) and Y (DDX3Y) chromosomes, albeit the latter is restricted to testes (1). It participates in different stages of cellular gene expression, such as transcription, mRNA maturation, and mRNA export and translation (2). Given these crucial roles in RNA biology, several RNA viruses interact with DDX3X, often with important consequences for viral replication. This includes hepatitis C virus (HCV), norovirus, West Nile virus, and Japanese encephalitis virus (3-7). This is also the case for HIV and hepatitis B virus (HBV), a peculiar DNA virus that relies on an RNA template and reversed transcription to replicate its genome (8,9). Furthermore, DDX3X also contributes to innate immunity against these viruses. For instance, DDX3X stimulates interferon (IFN) type I production by binding IKK (IB kinase epsilon) and TBK1 (tank-binding kinase 1), leading to IRF3 phosphorylation and activation (10,