Studies on the Heterogeneity of Lysine-rich Histones in Dividing Cells

The heterogeneity of the lysine-rich histone from several mammalian cells has been studied. The molecules were cleaved with N-bromosuccinimide and separated into three fractions by exclusion chromatography. The three fractions were Fraction 1, the NH2-terminal peptide of molecular weight ∼6000 which proved to be highly heterogeneous upon electrophoretic analysis; Fraction 2, the COOH-terminal fragment, which consists of two molecular weight groups (14,500 and 15,500), both of which are additionally heterogeneous as was deduced from tryptic fingerprinting and analysis of arginine-containing peptides; and Fraction 3, a protein which had the same molecular weight as the intact, unreacted lysine-rich histone. However, it did contain a spirolactone and we deduce that it is the product of an abnormal N-bromosuccinimide cleavage reaction. It shows the same type of electrophoretic heterogeneity as is seen for unreacted histone.