Functional interaction between Epstein-Barr virus DNA polymerase catalytic subunit and its accessory subunit in vitro

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Epstein-Barr virus (EBV) DNA polymerase is essential for viral replication.
• The holoenzyme consists of a catalytic subunit (BALF5) and an accessory subunit (BMRF1).
• Understanding subunit interactions is key to elucidating viral DNA synthesis mechanisms.

Purpose of the Study:

• To investigate the molecular basis of protein-protein interactions between EBV DNA polymerase subunits.
• To determine the role of the BMRF1 accessory subunit in BALF5 polymerase activity and processivity.
• To explore the mechanism by which BMRF1 influences EBV DNA replication.

Main Methods:

• Independent overexpression and purification of BALF5 and BMRF1 proteins.
• In vitro assays measuring DNA polymerase activity in the presence and absence of BMRF1.
• Ionic strength sensitivity assays and monoclonal antibody neutralization tests.
• Processivity assays using primed M13 single-stranded DNA circles.

Main Results:

• BALF5 polymerase activity alone was sensitive to high ionic strength.
• BMRF1 significantly enhanced BALF5 activity (10-fold stimulation) at high salt concentrations.
• Optimal stimulation occurred at a BMRF1:BALF5 molar ratio of ≥2.
• BMRF1 binding was confirmed by antibody neutralization assays.
• BMRF1 dramatically increased polymerization processivity from ~50 to >7,200 nucleotides.

Conclusions:

• The BMRF1 accessory subunit plays a critical role in enhancing EBV DNA polymerase activity and processivity.
• BMRF1 likely functions as a sliding clamp, stabilizing polymerase-DNA interaction.
• These findings provide molecular insights into the mechanism of EBV DNA replication.