Cell memory

Although most cells in a fission yeast colony suppress recombination and transcription around their mating loci, some of the cells fail to do so. In the April 28 Cell Nakayama et al. show that overproduction of Swi6 protein converts the mating locus of this latter class of cells to the transcription-off state (Cell 2000, 101:307-317). This imprinted state is heritable through both mitosis and meiosis, even after Swi6 is no longer overproduced. Deacetylated histone H4 is associated with the imprinted state, but the key to stable repression appears to be the binding of Swi6 to chromatin at the imprinted locus.