DIRECT BRLF1 BINDING IS REQUIRED FOR COOPERATIVE BZLF1 BRLF1 ACTIVATION OF THE EPSTEIN-BARR-VIRUS EARLY PROMOTER, BMRF1 (VOL 21, PG 1999, 1993)/

Disruption of Epstein-Barr virus (EBV) latency is mediated through the activation of the viral immediate-early proteins, BZLF1 (Z) and BRLF1 (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, 4085 - 4089). We have previously demonstrated that these proteins cooperat ively activate the EBV early promoter BMRF1 in lymphoid cells but not in epithelial cells. Although cooperative transactivation by these pro teins has been demonstrated with a number of EBV promoters, the mechan ism of this interaction is not well understood. We now show that the c ooperative activation of the BMRF1 promoter by Z-plus-R requires an in tact R binding site and at least one functional Z response element (ZR E). Despite the presence of an R binding site, the BMRF1 promoter is o nly moderately responsive to R alone in either HeLa or Jurkat cells. E fficient activation of the BMRF1 promoter by Z alone in HeLa cells req uires two ZREs (located at - 59 and - 106), whereas two additional Z b inding sites (located at - 42 and - 170) contribute very little to Z-i nduced activation. In the absence of ZREs, Z acted as a repressor of R -induced transactivation. These observations, along with observations made by other investigators (Giot, J.F. et al., (1991) Nucleic Acids R es., 19, 1251 - 8), suggest that Z-plus-R cooperative activation is de pendent upon 1) direct binding by R and Z to responsive promoter eleme nts and 2) contributions by cell-specific factors.