COOPERATION OF EBV DNA-POLYMERASE AND EA-D(BMRF1) INVITRO AND COLOCALIZATION IN NUCLEI OF INFECTED-CELLS

Expression of the Epstein-Barr virus (EBV) DNA polymerase (EBVpol) open reading frame (BALF5) byin vitro transcription-translation yielded a 116-kDa primary translation product. Enzymatic DNA polymerase activity of thein vitro translated polypeptide required the presence of the 47-kDa BMRF1 (EA-D) gene product. Antiserum raised to the BALF5 gene product expressed inEscherichia coli specifically precipitated a 116-kDa polypeptide in extracts of latently infected lymphoblastoid cells induced for EBV replication. Immunofluorescence microscopy revealed colocalization of the EBVpol and EA-D(BMRF1) to discrete foci within the nuclei of induced cells; however, the blockade of viral DNA synthesis resulted in diffuse nuclear staining patterns for both antigens. Bromodeoxyuridine staining of these discrete foci colocalizing with EBVpol suggests that they are sites of early viral DNA synthesis. These observations suggest that EA-D(BMRFl) may be an accessory protein of the EBV DNA polymerase which colocalizesin vivo with EBVpol to sites of viral DNA replication and cooperatesin vitro to form an active EBVpol holoenzyme. © 1991 Academic Press, Inc.