Plays an essential role in the viral lytic DNA replication by acting as the 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 early BHLF1 promoter (By similarity). Homodimer. Homooligomerizes and adopts an oligomeric ring-shaped structure composed of 6 subunits. Forms a complex with the DNA-binding protein BALF2, the DNA polymerase subunit BALF5, and the alkaline exonuclease BGLF5. Interacts with BZLF1; this interaction may inhibit BZLF1-induced transcription of the BMRF1 promoter (By similarity). BMRF1 shows homogeneous, not dot-like, distribution in the replication compartments, which coincides with the newly synthesized viral DNA. Phosphorylated by the viral BGLF4 kinase. Belongs to the herpesviridae DNA polymerase accessory subunit family.