Fig. 1. Reconstitution of nucleosome core particles. (A) Histone octamers isolated from chicken erythrocytes, consisting of equimolar amounts of the four core histones, shown after 18% acrylamide/SDS–gel electrophoresis and staining with Coomassie Brilliant Blue R. (B) The 146 bp fragment of the L.variegatus 5S rRNA gene containing a single uracil residue in position 19 (lane 1) was reconstituted into nucleosome core particles upon serial salt dilution in the presence of histone octamers, producing a characteristic band shift in a native 5% polyacrylamide gel (lane 2). (C) Naked DNA (DNA) and nucleosome core particles (NCP) containing a single uracil residue (U19) were subjected to DNase I footprinting using 0.2 (DNA) or 4 U of DNase I (NCP). Aliquots were removed after 0, 0.5, 1, 3, 6 and 15 (NCP only) min, denatured, and analysed in 8% polyacrylamide/7 M urea/20% formamide gels.