Acts as a DNA polymerase processivity factor; a transcriptional activator for several EBV promoters and inhibits the host DNA damage response (DDR) to double-stranded DNA breaks. Plays an essential role in the viral lytic DNA replication by acting as a polymerase accessory subunit. Stimulates the viral DNA polymerase activity and appears to function with it as a holoenzyme. Increases the processivity of the viral polymerase, probably by acting as a sliding clamp that prevents dissociation of the polymerase from the active template. In addition, BMRF1 transcriptionally activates the oriLyt early BHLF1 promoter. Promotes G1/S cell cycle arrest through p53 induction