Nucleolar disruption impairs Kaposi's sarcoma-associated herpesvirus ORF57-mediated nuclear export of intronless viral mRNAs.

Kaposi's sarcoma-associated herpesvirus (KSHV) ORF57 plays a pivotal role in mediating the nuclear export of KSHV intronless transcripts. We demonstrate that ORF57 localises and dynamically trafficks through the nucleolus. To assess if nucleolar shuttling of ORF57 is important for the export of intronless viral mRNA, the ability of ORF57 to export mRNA was assessed in cells where the nucleolus was disrupted using Actinomycin D or DRB. We show that rapid disorganisation of the nucleolus was accompanied by a reduction in intronless virus mRNA export, suggesting that an intact nucleolus is essential for efficient KSHV ORF57-mediated intronless mRNA export.