On the cover: In 1974, Olins and Olins (Science 183: 330–332) and Kornberg (Science 184: 868–871) were working to unravel the mystery of DNA packaging and observed that DNA was wrapped around repeated units of “spherical chromatin particles.” These “particles on a string” were nucleosomes, made up of an octamer of histones, and were determined to be the first step in the complicated process of condensation of linear DNA into chromatin. Although nucleosomes were initially thought to serve only as a means of DNA packaging, in 1988, Han and Grunstein reported initial in vivo evidence that the nucleosome was also involved in transcription regulation (Cell 55: 1137–1145). The image shows a 2.8 Å X-ray crystal structure of 146 base pairs of DNA wrapped around the nucleosome core (Nature 389: 251–260). The histone-protein main chains are represented by the different colored ribbons at the center of the circle of DNA. Adapted by permission from Macmillan Publishers Ltd: Nature 389: 251–260, copyright 1997. Special thanks to Dr. Timothy Richmond, ETH Zurich, Institut für Molekularbiologie und Biophysik, for the image.