Eb. Quinlivan et al., DIRECT BRLF1 BINDING IS REQUIRED FOR COOPERATIVE BZLF1 BRLF1 ACTIVATION OF THE EPSTEIN-BARR-VIRUS EARLY PROMOTER, BMRF1/, Nucleic acids research, 21(8), 1993, pp. 1999-2007
Disruption of Epstein - Barr virus (EBV) latency is mediated through t
he activation of the viral immediate-early proteins, BZLF1 (Z) and BRL
F1 (R).i.; (Chevallier-Greco, A., et al., (1 986) EMBO J., 5, 3243 - 9
; Countryman, and Miller, G. (1985) Proc. Natl. Acad. Sci. USA, 82, 40
85 - 4089). We have previously demonstrated that these proteins cooper
atively activate the EBV early promoter BMRF1 in lymphoid cells but no
t in epithelial cells. Although cooperative transactivation by these p
roteins has been demonstrated with a number of EBV promoters, the mech
anism of this interaction is not well understood. We now show that the
cooperative activation of the BMRF1 promoter by Z-plus-R requires an
intact R binding site and at least one functional Z response element (
ZRE). Despite the presence of an R binding site, the BMRF1 promoter is
only moderately responsive to R alone in either HeLa or Jurkat cells.
Efficient activation of the BMRF1 promoter by Z alone in HeLa cells r
equires two ZREs (located at - 59 and - 106), whereas two additional Z
binding sites (located at - 42 and - 170) contribute very little to Z
-induced activation. In the absence of ZREs, Z acted as a repressor of
R-induced transactivation. These observations, along with observation
s made by other investigators (Giot, J.F. et al., (1991) Nucleic Acids
Res., 19, 1251 - 8), suggest that Z-plus-R cooperative activation is
dependent upon 1) direct binding by R and Z to responsive promoter ele
ments and 2) contributions by cell-specific factors.