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J. Virol., Nov 1997, 8552-8562, Vol 71, No. 11
SA Radkov, M Bain, PJ Farrell, M West, M Rowe and MJ Allday
EBNA3C is a potent repressor of transcription when bound to DNA as a fusion
with the DNA binding domain (DBD) of GALA. A survey of promoters has
revealed that the wild-type, unfused EBNA3C can specifically repress
expression from reporter plasmids containing the Epstein-Barr virus Cp
latency-associated promoter. Repression of Cp activity required amino acids
207 to 368, which encompasses a region resembling a basic DBD adjacent to a
leucine zipper DNA binding motif and a site which binds to the cellular
factor CBF1/RBP-Jkappa. However, amino acids 207 to 368 are dispensable
when the protein is bound to DNA as a fusion with the GAL4 DBD, thus
implicating this region in DNA binding. Mutation of the CBF1/RBP-Jkappa
binding site in EBNA3C abrogated repression, strongly suggesting that
CBF1/RBP-Jkappa is necessary for targeting the viral protein to Cp.
Consistent with this result, mutation of the EBNA2 response element (a
CBF1/RBP-Jkappa binding site) in Cp also prevented significant repression.
In addition, amino acids 346 to 543, which were previously defined as
important for the repressor activity of the GAL4-EBNA3C fusion proteins,
also appear to be necessary for the repression of Cp. Since repression by
these fusions was not observed in all cell types, it seems likely that
EBNA3C either depends on a corepressor which may interact with amino acids
346 to 543 or is modified in a cell-specific manner in order to repress.
These data are consistent with EBNA3C contributing to the regulation of
EBNA expression in latently infected B cells through CBF1/RBP-Jkappa and
another factor, but this need not directly involve EBNA2. Finally, although
it has been reported that EBNA3C can upregulate CD21 in some B cells, we
were unable to demonstrate any effect of EBNA3C on reporter plasmids which
contain the CD21 promoter.
Copyright © 1997, American Society for Microbiology
Epstein-Barr virus EBNA3C represses Cp, the major promoter for EBNA expression, but has no effect on the promoter of the cell gene CD21
Department of Medical Microbiology, Imperial College School of Medicine at St Mary's, London, United Kingdom.
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