Histone H4 lysine 20 mono- and tri-methylation define distinct biological processes in SV40 minichromosomes

The methylation profile of histone H4 on lysine 20 in SV40 chromatin during an infection was investigated using ChIp analyses with antibodies to monomethyl (H4K20me1), dimethyl (H4K20me2), and trimethyl (H4K20me3) histone H4. H4K20me1 was found in late-transcribing, uncoating, encapsidating and replicating minichromosomes as well as in the SV40 chromatin present in virions. Its prevalence was greatest in virions and least in minichromosomes present between 4 and 24 hours post-infection. In contrast, H4K20me2 did not appear to be present and H4K20me3 appeared to be present only in minichromosomes obtained 30 minutes post-infection. The presence of H4K20me1 late in infection in replicating minichromosomes and its relative enrichment in virions suggested that it played a role in the encapsidation process. In contrast, the presence of H4K20me3 at the earliest stages of the infection and its subsequent relatively rapid loss along with sV40 chromatin suggested that it was functioning during the uncoating process.