Nucleosomal structure at hyperacetylated loci probed in nuclei by DNA-histone crosslinking.

Chemically induced histone-DNA crosslinking in nuclei is used to monitor structural changes in chromosomal domains containing hyperacetylated histones. Core particles harbouring the crosslinks are immunofractionated with antibodies specific for acetylated histones. Crosslinking is revealed by gel separation of tryptic peptides from core histones that carry 32P-labelled residual nucleotide. The large number of DNA-histone crosslinks retained indicates that acetylated core histone tails are not totally displaced from the DNA. Changes in the patterns of crosslinked peptides imply a restructuring of hyperacetylated histone-DNA interactions at several points within the nucleosome. This demonstrates that a distinct conformational state is adopted in acetylated nucleosomes, known to be concentrated at transcriptionally active loci.