Several recent studies have shown that a protein specific to centromeres—known as CENtromere Protein-A (CENP-A) in humans—is necessary across eukaryotes to preserve centromere location, but exactly how it does so has been unclear. Using a new technique, a group of researchers report in Nature this week that they have located a small stretch of human CENP-A that stiffens the centromere, creating an epigenetic mark that faithfully passes centromere identity to daughter cells.

CENP-A is a homolog of the nucleosomal protein histone H3, which forms tetramers with histone H4 throughout most genomic chromatin. At centromeres, however, CENP-A replaces H3. Ben Black, a postdoc at the Ludwig Institute for Cancer Research at the University of California, San Diego, and his colleagues used a new mass spectrometry technique to show that one region of CENP-A is much more compact than the homologous region of H3. This rigid region is an epigenetic tag,...

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