During lytic
infections, HSV-1 genomes are assembled into unstable
nucleosomes. The
histones required for HSV-1 chromatin assembly, however, are in the cellular
chromatin. We have shown that linker (H1) and core (H2B and H4)
histones are mobilized during HSV-1
infection, and proposed that the mobilized
histones are available for assembly into viral
chromatin. However, the actual relevance of
histone mobilization remained unknown. We now show that canonical H3.1 and variant H3.3 are also mobilized during HSV-1
infection. Mobilization required no HSV-1
protein expression, although immediate early or early
proteins enhanced it. We used the previously known differential association of H3.3 and H3.1 with HSV-1
DNA to test the relevance of
histone mobilization. H3.3 binds to HSV-1 genomes first, whereas H3.1 only binds after HSV-1 DNA replication initiates. Consistently, H3.3 and H3.1 were differentially mobilized. H3.1 mobilization decreased with HSV-1 DNA replication, whereas H3.3 mobilization was largely unaffected by it. These results support a model in which previously mobilized H3.1 is immobilized by assembly into viral
chromatin during HSV-1 DNA replication, whereas H3.3 is mobilized and assembled into HSV-1
chromatin throughout
infection. The differential mobilizations of H3.3 and H3.1 are consistent with their differential assembly into viral
chromatin. These data therefore relate nuclear
histone dynamics to the composition of viral
chromatin and provide the first evidence that
histone mobilization relates to viral chromatin assembly.