In eukaryotes, epigenetic events govern diverse processes, ranging from gene expression to other aspects of global chromosome architecture essential for preserving the integrity of the genome. Transcriptional silencing at the mating-type locus, centromeres, and telomeres of the fission yeast is regulated by epigenetic mechanisms. Epigenetic states are inherited in cis during mitosis and, remarkably, even through meiosis. Several trans-acting genes 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 study showed that Swi6 is involved in imprinting at the mating-type locus and contributes to the cellular memory responsible for maintenance of the silenced state. The "gene" in this instance thus comprises DNA plus the associated Swi6-containing protein complex.
Copyright 2000 Wiley-Liss, Inc.