Johansson, Erik

How cells ensure symmetric inheritance Parental histones with modifications are recycled to newly replicated DNA strands during genome replication, but do the two sister chromatids inherit modified histones equally? Yu et al. and Petryk et al. found in mouse and yeast, respectively, that modified histones are segregated to both DNA daughter strands in a largely symmetric manner (see the Perspective by Ahmad and Henikoff). However, the mechanisms ensuring this symmetric inheritance in yeast and mouse were different. Yeasts use subunits of DNA polymerase to prevent the lagging-strand bias of parental histones, whereas in mouse cells, the replicative helicase MCM2 counters the leading-strand bias. Science , this issue p. 1386 , p. 1389 ; see also p. 1311