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Viruses 2015, 7(2), 604-633;

KSHV ORF57, a Protein of Many Faces

Tumor Virus RNA Biology Section, Gene Regulation and Chromosome Biology Laboratory, National Cancer Institute, National Institutes of Health, 1050 Boyles Street, Frederick, MD 21702, USA
Author to whom correspondence should be addressed.
Academic Editor: Eric O. Freed
Received: 29 November 2014 / Accepted: 2 February 2015 / Published: 10 February 2015
(This article belongs to the Special Issue Kaposi's Sarcoma-Associated Herpesvirus)
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Kaposi’s sarcoma-associated herpesvirus (KSHV) ORF57 protein (also known as mRNA transcript accumulation (Mta)) is a potent posttranscriptional regulator essential for the efficient expression of KSHV lytic genes and productive KSHV replication. ORF57 possesses numerous activities that promote the expression of viral genes, including the three major functions of enhancement of RNA stability, promotion of RNA splicing, and stimulation of protein translation. The multifunctional nature of ORF57 is driven by its ability to interact with an array of cellular cofactors. These interactions are required for the formation of ORF57-containing ribonucleoprotein complexes at specific binding sites in the target transcripts, referred as Mta-responsive elements (MREs). Understanding of the ORF57 protein conformation has led to the identification of two structurally-distinct domains within the ORF57 polypeptide: an unstructured intrinsically disordered N-terminal domain and a structured α-helix-rich C-terminal domain. The distinct structures of the domains serve as the foundation for their unique binding affinities: the N-terminal domain mediates ORF57 interactions with cellular cofactors and target RNAs, and the C-terminal domain mediates ORF57 homodimerization. In addition, each domain has been found to contribute to the stability of ORF57 protein in infected cells by counteracting caspase- and proteasome-mediated degradation pathways. Together, these new findings provide insight into the function and biological properties of ORF57 in the KSHV life cycle and pathogenesis. View Full-Text
Keywords: KSHV; ORF57 protein; viral expression; posttranscriptional regulator; RNA processing KSHV; ORF57 protein; viral expression; posttranscriptional regulator; RNA processing

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Majerciak, V.; Zheng, Z.-M. KSHV ORF57, a Protein of Many Faces. Viruses 2015, 7, 604-633.

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