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The 11 th International Workshop on KSHV & Related Agents, Birmingham, UK
Lytic Replication Abstract 41
KSHV ORF57 ENHANCES TRANSLATION OF VIRAL INTRONLESS MRNAS
James R. Boyne, Adam Taylor and Adrian Whitehouse
Institute of Molecular and Cellular Biology, University of Leeds, Leeds, LS2 9JT, United
Kingdom
Abstract
The majority of Kaposi’s sarcoma associated herpesvirus (KSHV) mRNAs lack introns and
are exported by the ORF57 protein. We have shown that ORF57 binds specifically to
intronless viral mRNAs and functions to recruit the human TREX (hTREX) complex, in
contrast to the exon-junction complex, allowing efficient nuclear export of the viral
intronless mRNAs. The failure of ORF57 to recruit EJC components to viral intronless
mRNAs presents KSHV with an intriguing problem, as the EJC enhances translation of
cellular spliced mRNAs. The EJC specifically recruits the translation machinery onto the
mRNA via an interaction with the cellular protein PYM, thereby enhancing mRNA
translation. Herein, we demonstrate that KSHV ORF57 functions in translation
enhancement, bypassing the EJC, by recruiting essential cellular translation factors. We
shown, using an in vitro translation assay, that recombinant KSHV ORF57 can enhance
translation of an in vitro transcribed KSHV intronless RNA. Moreover, coimmunoprecipitation
assays demonstrate that KSHV ORF57 interacts with PYM and 48S
preinitiation components in an RNA-independent manner in both transfected and
reactivated BCBL cells. Furthermore, GST-pulldown analysis shows that ORF57 only
associates directly with PYM and no other members of the 48S preinitiation complex. This
suggests that KSHV ORF57 enhances translation by recruiting the 48S preinitiation
complex onto a viral intronless mRNA lacking an EJC, via its direct interaction with PYM.
This data highlights a new role for the ORF57 protein in the KSHV lytic replication cycle.
Presenting author Email: A.Whitehouse@leeds.ac.uk
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