Transcriptional silencing in fission yeast

In eukaryotes, epigenetic events govern diverse processes, ranging from gen e expression to other aspects of global chromosome architecture essential f or preserving the integrity of the genome. Transcriptional silencing at the mating-type locus, centromeres, and telomeres of the fission yeast is regu lated by epigenetic mechanisms. Epigenetic states are inherited in cis duri ng mitosis and, remarkably, even through meiosis. Several trans-acting gene s that affect silencing are found to encode either chromatin proteins such as chromodomain proteins Swi6 and Clr4 or the factors that affect chromatin assembly, including histone deacetylase homologs Clr3 and Clr6. A recent s tudy showed that Swi6 is involved in imprinting at the mating-type locus an d contributes to the cellular memory responsible for maintenance of the sil enced state. The "gene" in this instance thus comprises DNA plus the associ ated Swi6-containing protein complex, J. Cell. Physiol. 184:311-318, 2000. (C) 2000 Wiley-Liss, Inc.