During viral infection, the amount of viral mRNAs expressed is not only a reflection of the viral gene transcription level: mRNA stability and nucleo-cytoplasmic export are also important for optimal viral gene expression during the productive cycle. It is now well established that herpesviruses express a protein absolutely required for the cytoplasmic accumulation of some viral mRNAs transcribed from intronless genes. This family of proteins comprises the EB2 factor from Epstein-Barr virus (EBV), and its similar proteins: ICP27 from HSV-1, UL69 from cytomegalovirus (CMV), ORF57 from KSHV and IE4 from VZV. These proteins are able to stabilize their target mRNAs in the nucleus and, by interacting with various cellular factors (TAP/NXF1, SR proteins, RBM15 etc), promote mRNA export to the cytoplasm, where they are also involved in the translation efficiency of these viral mRNAs. On the basis of their essential role in the viral productive cycle, these multifunctional viral factors should be considered as important targets for therapeutic approaches.
Keywords: herpesvirus; mRNA export; post-transcriptional regulation; productive cycle.