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Journal of Virology, December 1999, p. 9858-9866, Vol. 73, No. 12
Departments Molecular Biophysics and
Biochemistry,1
Pediatrics,2 and Epidemiology
and Public Health,3 Yale University School
of Medicine, New Haven, Connecticut 06520
Received 28 May 1999/Accepted 23 August 1999
Initiation of the Epstein-Barr virus (EBV) lytic cycle is
controlled by two immediate-early genes, BZLF1 and BRLF1. In certain epithelial and B-cell lines, their protein products, ZEBRA and Rta,
stimulate their own expression, reciprocally stimulate each other's
expression, and activate downstream viral targets. It has been
difficult to examine the individual roles of these two transactivators
in EBV-infected lymphocytes, as they are expressed simultaneously upon
induction of the lytic cycle. Here we show that the Burkitt lymphoma
cell line Raji represents an experimental system that allows the study
of Rta's role in the lytic cycle of EBV in the absence and presence of
ZEBRA. When expressed in Raji cells, exogenous Rta does not activate
endogenous BZLF1 expression, yet Rta remains competent to transactivate
certain downstream viral targets. Some genes, such as BaRF1, BMLF1, and
a late gene, BLRF2, are maximally activated by Rta itself in the
absence of detectable ZEBRA. The use of the Z(S186A) mutant form of
ZEBRA, whose transactivation function is manifest only by coexpression of Rta, allows identification of a second class of lytic cycle genes,
such as BMRF1 and BHRF1, that are activated in synergy by Rta and
ZEBRA. It has already been documented that of the two activators, only
ZEBRA stimulates the BRLF1 gene in Raji cells. Thus, there is a third
class of viral genes activated by ZEBRA but not Rta. Moreover, ZEBRA
exhibits an inhibitory effect on Rta's capacity to stimulate the late
gene, BLRF2. Consequently ZEBRA may function to repress Rta's
potential to activate some late genes. Raji cells thus allow
delineation of the combinatorial roles of Rta and ZEBRA in control of
several distinct classes of lytic cycle genes.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Role of the Epstein-Barr Virus Rta Protein in
Activation of Distinct Classes of Viral Lytic Cycle Genes
*
Corresponding author. Mailing address: Department of
Pediatrics, Yale University School of Medicine, 333 Cedar St., New
Haven, CT 06520. Phone: (203) 785-4758. Fax: (203) 785-6961. E-mail: George.Miller{at}yale.edu.
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