Parental nucleosomes segregated to newly replicated chromatin are underacetylated relative to those assembled de novo

Antibodies specific for acetylated histone H4 were used to examine the acetylation state of parental histones that segregate to newly replicated DNA. To generate newly replicated chromatin containing only segregated parental nucleosomes, isolated nuclei were labeled with [ 3 H]TTP in vitro; alternatively, whole cells were labeled with [ 3 H]thymidine in the presence of cycloheximide. Soluble chromatin was prepared by micrococcal nuclease digestion, and subjected to immunoprecipitation with «penta» antibodies (Lin et al., 1989). In sharp contrast to nucleosomes containing newly synthesized, diacetylated H4 (Perry et al., 1993), chromatin replicated in vitro was only marginally susceptible to immunoprecipitation