from Jeffery L. Meier and Mark F. Stinski writing in Cytomegaloviruses: From Molecular Pathogenesis to Intervention:
CMV major immediate-early (MIE) gene expression activates the viral replicative cycle in both acute and reactivation infections and is greatly restricted in latent infection. Specific signaling cascades, transcriptional regulatory hierarchies, and cis-regulatory codes govern the initiation efficacy, magnitude, and sustainability of MIE gene transcription. The MIE enhancer/promoter, a major determinant in viral fitness, is at the heart of this control. It is equipped with complex regulatory circuitry that integrates diverse viral, cellular, and environmental cues. The MIE genes via differential RNA splicing produce a set of multifunctional proteins that function directly in advancing the viral life cycle. CMV-induced disease genesis is driven by the regulatory mechanisms underlying both the expression of the MIE genes and the actions of the MIE gene products. A better understanding of the MIE enhancer and its gene products could potentially spawn novel strategies for preventing CMV-related disease.
Further reading: Cytomegaloviruses: From Molecular Pathogenesis to Intervention