Solo or doppio: how many CENP-As make a centromeric nucleosome?

Whether centromere-specific CENP-A–containing nucleosomes comprise one molecule each of CENP-A and histones H4, H2A and H2B (forming a tetramer or hemisome) or two molecules of all four histones (forming an octamer) has been controversial. Three new studies now address this controversy using complementary in vitro and in vivo approaches.