Bisection of a Lysine-rich Histone by N-Bromosuccinimide

A homogeneous rabbit thymus lysine-rich histone was cleaved between a tyrosine residue and an aspartic acid (or asparagine) residue by N-bromosuccinimide. The carboxyl-terminal portion (molecular weight 15,000) was richer in lysine than the amino-terminal portion (molecular weight 6,000). This enrichment of lysine residues toward the carboxyl-terminal part of the molecule is apparently characteristic of all the subfractions in calf thymus as well as in rabbit thymus lysine-rich histones. Preliminary data suggest that the amino-terminal portion of these molecules is the location of most of the differences in primary structure from one subfraction to another.