NUCLEOSOMAL STRUCTURE AT HYPERACETYLATED LOCI PROBED IN NUCLEI BY DNAHISTONE CROSS-LINKING

Chemically induced histone-DNA crosslinking in nuclei is used to monit or structural changes in chromosomal domains containing hyperacetylate d histones. Core particles harbouring the crosslinks are immunofractio nated with antibodies specific for acetylated histones. Crosslinking i s revealed by gel separation of tryptic peptides from core histones th at carry P-32-labelled residual nucleotide. The large number of DNA-hi stone crosslinks retained indicates that acetylated core histone tails are not totally displaced from the DNA. Changes in the patterns of cr osslinked peptides imply a restructuring of hyperacetylated histone-DN A interactions at several points within the nucleosome. This demonstra tes that a distinct conformational state is adopted in acetylated nucl eosomes, known to be concentrated at transcriptionally active loci.