How Epstein-Barr Virus Induces the Reorganization of Cellular Chromatin

Abstract

We have discovered how Epstein-Barr virus (EBV) induces the reorganization of cellular chromatin (ROCC), in which host chromatin is compacted and marginated within the nucleus, with viral DNA replication occurring in the chromatin-free regions. Five families of DNA viruses induce ROCC: herpesviruses, adenoviruses, parvoviruses, baculoviruses, and geminiviruses. These families infect a variety of hosts, including vertebrates, insects, and plants. They also share several characteristics: they replicate and encapsidate their genomes in the host nucleus and package their genomes unbound by histones. We have identified the viral genes and processes required for EBV's ROCC. Each of EBV's seven core DNA synthesis genes and its origin of lytic replication (oriLyt), in trans, are required, while its protein kinase, BGLF4, and its true late genes are not. Following these findings, we tested the role of EBV lytic DNA amplification in driving ROCC. Surprisingly, the inhibition of EBV's lytic DNA synthesis still supports chromatin compaction but blocks its margination. We propose a two-step model for ROCC. First, the initiation of viral lytic DNA synthesis induces a cellular response that results in global chromatin compaction. Second, the histone-free, productive viral DNA synthesis leads to the margination of compacted chromatin to the nuclear periphery. We have tested this model by asking if the histone-associated simian virus 40 (SV40) DNA synthesis could substitute for oriLyt-mediated synthesis and found that EBV's ROCC is incompatible with SV40 DNA replication. Elucidating EBV's induction of ROCC both illuminates how other viruses can do so and indicates how this spatial control of cellular chromatin benefits them.