Temporal Control of Histone H4 methylation in SV40 minichromosomes during lytic infection

Abstract

Acetylation and methylation of histones are known to play critical roles in many biological processes. We have previously shown that in the coding region of a transcribing SV40 minichromosome, histone hyperacetylation is a dynamic process regulated by the interplay of p300, a histone acetyltransferase and a histone deacetylase, co migrating along with the transcription complex. Our current studies are focused on histone H4 methylation in SV40 minichromosomes. Histone H4 is known to undergo mono, di, or tri methylation of lysine 20 (H4K20me1, H4K20me2, and H4K20me3 respectively) with differing biological effects. Using various chromatin immunoprecipitation procedures we have determined that minichromosomes containing H4K20me1 were present throughout an SV40 infection, and minichromosomes containing H4K20me3 were present only during the first hours of infection. Minichromosomes containing H4K20me2 were not present in infected cells. Combining ChIP analysis with tritiated thymidine pulse radiolabeling of chromatin we observed direct evidence for conservation of histone methylation in daughter minichromosomes following replication. In contrast to our results with histone hyperacetylation in SV40 minichromosomes, methylation of H4K20 appears to define a small conserved stable subclass of minichromosomes with the potential to participate in various biological functions.