Functional co-operation between the Kaposi's sarcoma-associated herpesvirus ORF57 and ORF50 regulatory proteins

Poonam Malik, David J. Blackbourn, Ming Fei Cheng, Gary S. Hayward, J. Barklie Clements*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)


Kaposi's sarcoma (KS)-associated herpesvirus (KSHV) proteins ORF57 (also known as MTA) and ORF50 (also known as RTA) act post-transcriptionally and transcriptionally to regulate viral lytic gene expression and synergistically activate certain early and late KSHV promoters. When ORF57 and ORF50 were co-expressed, they co-operatively stimulated expression from the promoter of the immediate-early ORF50 gene itself. Co-immunoprecipitations with extracts of KSHV-infected cells showed that ORF57 and ORF50 proteins were present in the same complex. Using the pull-down assay with extracts of KSHV-infected cells, ORF50 protein was shown to interact with a glutathione S-transferase-ORF57 fusion protein. A chromatin immunoprecipitation assay showed that ORF50 promoter sequences were preferentially associated with immunoprecipitated chromatin using both anti-ORF50 and anti-ORF57 antibodies consistent with both an in vivo physical association between ORF57 and ORF50 and a potential role for ORF57 at the transcriptional level. This is the first demonstration of an interaction between these two lytic regulatory proteins in a gammaherpesvirus. Expression of ORF50 protein is sufficient to induce lytic replication in latently infected cells and may determine viral host range, spread and KS pathogenesis in vivo. A new insight into the co-ordinated activities of these two key regulatory proteins is provided in which upregulation of the ORF50 promoter with augmentation of ORF50 activity by ORF57 protein, and vice versa, would facilitate the cascade of lytic viral gene expression, thereby breaking latency. A functional and physical interaction between these two gammaherpesvirus regulatory protein counterparts could be a general feature of the herpesviruses.

Original languageEnglish
Pages (from-to)2155-2166
Number of pages12
JournalJournal of General Virology
Issue number8
Publication statusPublished - Aug 2004

Bibliographical note

This work was supported by an award from the Medical Research Council to J. B. C. (G9826324) and in part by grants to D. J. B. from the Wellcome Trust (059008/Z/99/Z) and the Association for International Cancer Research (01/242). P. M. was the recipient of a UK Commonwealth Postgraduate Scholarship. Thanks go to Dr Nigel Stow for comments on the manuscript.


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