BIPARTITE DNA-BINDING REGION OF THE EPSTEIN-BARR-VIRUS BMRF1 PRODUCT ESSENTIAL FOR DNA-POLYMERASE ACCESSORY FUNCTION

The Epstein-Barr virus (EBV) BMRF1 gene product is necessary for DNA p olymerase catalytic subunit (BALF5) activity in 100 mM ammonium sulfat e. To map regions of BMRF1 necessary for polymerase accessory function , linker insertion and deletion mutant BMRF1 polypeptides were express ed by in vitro transcription-translation and assayed for DNA polymeras e elongation activity and binding to double-stranded DNA (dsDNA)-cellu lose. Amino-terminal deletions up to residue 303 were defective for st imulation of elongation. Deletions between residues 44 and 194 and res idues 238 and 303 abolished binding to dsDNA-cellulose. The region fro m residues 194 to 238, therefore, is necessary for stimulation of BALF 5 elongation but dispensable for dsDNA-cellulose binding. Deletion ana lysis also localized reactive epitopes of two neutralizing monoclonal antibodies to BMRF1 to a carboxy-terminal region which is dispensable for activity. These data suggest that a bipartite DNA-binding region i s an essential component of the DNA polymerase accessory function and that the two noncontiguous regions are separated by a region (residues 194 to 217) which is essential for stimulation; therefore, it may int eract with the BALF5 catalytic subunit of EBV DNA polymerase. Both EBV BMRF1 and herpes simplex virus UL42 gene products are DNA polymerase accessory proteins which bind dsDNA and increase the processivity of t heir corresponding catalytic components. Outstanding similarities betw een their primary amino acid sequences are not evident. However, it ap pears that their structural organizations are similar.