A complete chromosome set must be apportioned to each daughter cell during cell division. A number of molecular mechanisms check that chromosome pairs or homologs are correctly aligned and attached to microtubules just before they separate to the two daughters; their spatial orientation ensures an even inheritance of the genome. One critical component of this system is the protein kinase Bub1. Kawashima et al. (see the Perspective by Javerzat) now show that the main substrate for Bub1 kinase activity in fission yeast is the chromatin protein histone H2A. Phosphorylation of H2A recruits the shugoshin proteins to chromatin, and especially to centromeres, where they also act to ensure correct chromosome segregation. This link between Bub1, histone H2A phosphorylation, and shugoshin is conserved in budding yeast and mammalian cells.
S. A. Kawashima, Y. Yamagishi, T. Honda, K. Ishiguro, Y. Watanabe, Phosphorylation of H2A by Bub1 prevents chromosomal instability through localizing shugoshin. Science 327, 172–177 (2010). [Abstract] [Full Text]