Six degrees of separation

摘要

In chromosomes, a series of protein particles act like spools, packaging DNA into a structure called chromatin. The spools are known as nucleosomes, and most are composed of eight subunits - two subu-nits of each of the four major histone proteins, H2A, H2B, H3 and H4. However, the centromeric sites, which are required for chromosome segregation during cell division, are different. Instead of two subunits of H3, centromeric nucleosomes contain the centromere-specific histone H3 variant called CENP-A. Two papers1'2, including one by Guse et al. on page 354 of this issue, provide structural and mechanistic insights into the workings of CENP-A-containing nucleosomes.