Histone modifications before and after nucleosome assembly

摘要

Histone post-translational modifications that accompany DNA replication and chromatin assembly were examined in human tissue culture cells. Immunoprecipitations of [~3H]thymidine-labeled newly replicated mononucleosomes demonstrated the presence of specific acetylation and meth-ylation patterns of H3 and H4 on new DNA. Microsequenc-ing analysis and chromatin immunoprecipitation further showed that a subset of newly synthesized H3.2/H3.3 is modified by acetylation and methylation at sites that corre- late with transcriptional competence. In addition, all nascent H3 variants were deposited in chromatin regions containing K5/K12-acetylated H4. Finally, cytosolic predeposition complexes purified from synchronized cells provided evidence for the preferential acetylation of H3.2 and H3.3 prior to histone deposition. Our experiments provide an in-depth analysis of the histone code associated with chromatin replication and histone deposition in human cells.