Regulation of Epstein-Barr virus origin of plasmid replication (OriP) by the S-phase checkpoint kinase Chk2.

The Epstein-Barr virus (EBV) origin of plasmid replication (OriP) is required for episome stability during latent infection. Telomere repeat factor 2 (TRF2) binds directly to OriP and facilitates DNA replication and plasmid maintenance. Recent studies have found that TRF2 interacts with the DNA damage checkpoint protein Chk2. We show here that Chk2 plays an important role in regulating OriP plasmid stability, chromatin modifications, and replication timing. The depletion of Chk2 by small interfering RNA (siRNA) leads to a reduction in DNA replication efficiency and a loss of OriP-dependent plasmid maintenance. This corresponds to a change in OriP replication timing and an increase in constitutive histone H3 acetylation. We show that Chk2 interacts with TRF2 in the early G(1)/S phase of the cell cycle. We also show that Chk2 can phosphorylate TRF2 in vitro at a consensus acceptor site in the amino-terminal basic domain of TRF2. TRF2 mutants with a serine-to-aspartic acid phosphomimetic substitution mutation were reduced in their ability to recruit the origin recognition complex (ORC) and stimulate OriP replication. We suggest that the Chk2 phosphorylation of TRF2 is important for coordinating ORC binding with chromatin remodeling during the early S phase and that a failure to execute these events leads to replication defects and plasmid instability.