Histones bound to gene-sized pieces of DNA in the macronucleus of Oxytricha sp. consist of five main fractions: f1, f2a1, f2a2, f2b and f3. Although the slightly lysine-rich and the arginine-rich histones in Oxytricha macronuclei are similar to comparable fractions in vertebrates, the lysine-rich f1 fraction differs. Oxytricha f1 is unique among eukaryotes in that it migrates faster than f2a1 and is located nearest the cathode in polyacrylamide-urea gels.