Studies on Histone Oligomers I. Reconstitution and Fractionation of

Histone oligomers were reconstituted from calf thymus whole histones by annealing from 2 M NaCl-5 M urea-0.05 M Tris buffer (pH 8.0)-l %)3-mercaptoethanol, and were fractionated in terms of solubility in ammonium sulfate solution. Fractionation occurred according to the histone compositions of oligomers. The oligomers thus obtained were (1) pentamer and trimer of HI, (2) tetramer of H2A and H2B, and (3) tetramer and higher aggregates of H3 and H4, under the following ionic conditions: 0.5 M NaCl-0.05 M phosphate buffer (pH 7.0). The aggregates of H3 and H4 could easily be converted to the tetramer by lowering of pH. Recent progress in chromatin chemistry has shown that histones in chromatin exist as oligomers, probably as octamers of (H2A), • (H2B), • (H3), • (H4),, to form the core of nucleosomes (7). Most of the studies were done by analysis of cross-linked products of histones in chromatin or in solution (2-5). Many kinds of cross-linked histone oli-gomers up to octamer level were found in chro