Post-translational histone modifications - histone codes - specify local chromatin environments that control chromosome function during the cell cycle. Widespread phosphorylation of histone H3 during mitosis by the kinase Aurora B, for example, helps ensure accurate chromosome segregation. However, in G2 phase, H3 phosphorylation occurs only at pericentromeres (heterochromatin domains near the centromeres) because Aurora B is restricted to this region. Karine Monier and co-authors now report that DNA methylation promotes this pattern (see ). The authors show that histone H3 phosphorylation at pericentromeres starts in late S phase, persists into G2 phase and requires Aurora B activity. Using immunofluorescence in situ hybridization, they show that Aurora B and phosphorylated histone H3 are more abundant at large pericentromeres (where there is a high density of methyl cytosine) than at small ones. Finally, they report that disruption of DNA methylation prevents the localization of Aurora B to pericentromeres. Thus, the authors conclude, DNA methylation targets Aurora B to pericentromeres during interphase. Because tumour cells are often hypomethylated, they propose that mislocalization of Aurora B could contribute to chromosomal instability in cancer.
