from Robert F. Kalejta writing in Cytomegaloviruses: From Molecular Pathogenesis to Intervention:
As virions disassemble during viral entry, they must expertly navigate and manage the complex and unwelcoming environments they encounter in order to successfully infect host cells. Herpesviruses incorporate proteins into their virions in a layer between the capsid and envelope termed the tegument to assist in this hostile takeover. When delivered to infected cells subsequent to membrane fusion, tegument proteins begin to facilitate viral infection after entry but before immediate early (IE) gene expression (referred to as the pre-IE stage of infection). Tegument-delivered proteins mediate capsid migration through the cytoplasm to nuclear pore complexes and the transmission of the genome into the nucleus. Furthermore, they modulate viral transcription, and help infected cells avoid all three classes of immune function (intrinsic, innate and adaptive). While they are most often studied during lytic infections, a new appreciation for the role that the proper regulation of tegument-delivered protein function may play during viral latency is emerging. Here the pre-IE functions of tegument proteins during both lytic and latent infections are reviewed and analyzed.
Further reading: Cytomegaloviruses: From Molecular Pathogenesis to Intervention