As discussed above for Rev, it has been shown that the Herpes virus saimiri ORF57 protein is required for nuclear export of viral intronless mRNAs (Boyne and Whitehouse 2006) . In addition, the expression of ORF57 induces nuclear traYcking, which is essential for nuclear export of such RNAs; the human transcription/export protein involved in mRNA export, is redistributed to the nucleolus in the presence of the ORF57 protein. Based on these Wndings, the authors concluded that the nucleolus is required for nuclear export of the viral mRNAs.