In this issue of Cell, English et al. present the first crystal structure of a 
histone chaperone (Asf1) bound to histones (the H3/H4 heterodimer). The 
structure provides insights into how histone chaperones participate in 
nucleosome disassembly. It reveals that Asf1 physically blocks (H3/H4)(2) 
tetramer formation and that the C terminus of H4 undergoes a dramatic 
conformational change upon binding to Asf1.